 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued October 6, 2015                 Decided August 5, 2016

                         No. 14-1215

          ORY ESHEL AND LINDA CORYELL ESHEL,
                     APPELLANTS

                             v.

      COMMISSIONER OF INTERNAL REVENUE SERVICE,
                      APPELLEE


                   On Appeal from the
                  United States Tax Court


     Stuart E. Horwich argued the cause and filed the briefs
for appellants.

     Julie Ciamporcero Avetta, Attorney, U.S. Department of
Justice, argued the cause for appellee. With her on the brief
was Bridget M. Rowan, Attorney. Andrew Weiner, Attorney,
entered an appearance.

    Before: GRIFFITH, MILLETT, and PILLARD, Circuit
Judges.

    Opinion for the Court filed by Circuit Judge MILLETT.
                               2
     MILLETT, Circuit Judge: As a general rule, workers in
the United States are taxed to support the payment of social
security benefits to the retired and to individuals with
disabilities. The expectation is that, having contributed to the
national economy while actively employed, those workers
will later become eligible beneficiaries rather than supporters
of the social security system. See Flemming v. Nestor, 363
U.S. 603, 608–610 (1960).

    That system gets complicated, however, for Americans
who work overseas for part of their careers and, during those
years, are required to pay taxes into a foreign government’s
social security system.       Foreign workers temporarily
employed within the United States can sometimes confront a
similar problem.

     With Congress’s blessing, Presidents have entered into
so-called “totalization agreements” with foreign governments
to limit social-security taxing rights to the country where the
work is being done. The agreements also allow overseas
workers from both countries to obtain social security benefits
based on the periods for which they make social security
contributions to foreign governments.

     This case involves a totalization agreement between the
United States and France. Specifically, the issue on appeal is
whether or not two French taxes enacted into law after that
totalization agreement was adopted “amend[] or
supplement[]” the French social security laws covered by the
agreement, and thus fall within the agreement’s ambit. The
tax court declared the status of those French laws not by
analyzing the text of the totalization agreement or the
understanding of the parties, but by resorting to American
dictionaries. That was legal error. Because insufficient
consideration was given to the text and the official views of
                               3
the United States and French governments, we reverse and
remand.
                            I

                               A

     In 42 U.S.C. § 433, Congress authorized the President to
enter into social security coordination agreements—known as
totalization agreements—with other countries, see id.
§ 433(a). Absent such agreements, workers who divide their
careers among and pay taxes to multiple countries might pay
into the social security systems of various nations, yet fail to
qualify for benefits under any one system. Totalization
agreements permit those workers to combine periods of
payment into different countries’ social security systems to
eventually become eligible to receive benefits under a
signatory country’s system. Workers’ wages and self-
employment income are generally exempt from United States
social-security taxation to the extent that they are subject to
foreign social-security taxation. See 26 U.S.C. §§ 1401(c),
3101(c), 3111(c).

     Section 433 treats contributions to different countries’
social security systems as establishing “periods of coverage,”
which are “period[s] of payment of contributions or [periods]
based on wages for employment or on self-employment
income[.]” 42 U.S.C. § 433(b)(2). Under a totalization
agreement, employment creates a “period of coverage” under
the social security system of one of the two signatories, but
not both. Id. § 433(c)(1)(B)(i). That is, under Section 433, a
citizen working in a foreign country makes payments to—and
accrues periods of coverage under—only one social security
system at a time.
                               4
     Periods of coverage accrued under a foreign system may
be combined with periods of coverage under the United States
system “for the purposes of establishing entitlement” to
United States social security benefits.          42 U.S.C.
§ 433(c)(1)(A). An individual may also qualify for separate
benefit payments from multiple countries, in which case the
benefits payable by each system are based on the proportion
of the taxpayer’s total periods of coverage accrued in each
system. Id. § 433(c)(1)(C). Thus taxpayers whose careers
take them from the United States to other countries do not
suffer a diminution in their social security benefits upon
retirement.

     The United States generally taxes income earned by its
citizens regardless of where the citizen resides, but a United
States citizen may take a tax credit against his or her United
States income tax liability for taxes paid to a foreign country.
26 U.S.C. §§ 901(a) & (b). That credit shields taxpayers from
double taxation. In contrast, taxes paid to a foreign country in
accordance with a social security totalization agreement are
not eligible for such a tax credit:

    Notwithstanding any other provision of law, taxes
    paid by any individual to any foreign country with
    respect to any period of employment or self-
    employment which is covered under the social
    security system of such foreign country in
    accordance with the terms of an agreement entered
    into pursuant to section 233 of the Social Security
    Act [42 U.S.C. § 433] shall not, under the income
    tax laws of the United States, be deductible by, or
                               5
    creditable against the income tax of, any such
    individual.

26 U.S.C. § 1401 note.

     Under that provision, a foreign tax will not be eligible for
a tax credit if it is paid (i) with respect to a period of
employment covered under the social security system of a
foreign country, and (ii) “in accordance with” the terms of a
totalization agreement. See Erlich v. United States, 104 Fed.
Cl. 12, 17 (2012) (A tax is not creditable under this section
when the “payment is consistent with the obligation of the
taxpayer under the [totalization] agreement.”).

                               B

    In 1987, the United States and France entered into a
social security totalization agreement (“Totalization
Agreement”). See Agreement on Social Security Between the
United States of America and the French Republic, March 2,
1987, 2260 U.N.T.S. 145, available at https://
www.ssa.gov/international/Agreement_Texts/french.html. In
Article 2(1), the Totalization Agreement identifies the laws of
each country under which qualifying taxes may be paid. The
covered United States laws are specified provisions of the
Social Security Act and the Internal Revenue Code. 1 The
covered French laws are eight enumerated categories of

1
   Specifically, the covered provisions of United States law are:
“Title II of the Social Security Act and regulations pertaining
thereto, except sections 226, 226A and 228 of that title and
regulations pertaining to those sections,” and “Chapter 2 and
Chapter 21 of the Internal Revenue Code of 1986 and regulations
pertaining to those chapters[.]” Totalization Agreement, Art.
2(1)(a).
                                 6
French social security laws. 2 The Totalization Agreement
also covers taxes paid under “legislation which amends or
supplements the laws specified[.]” Totalization Agreement,
Art. 2(3).

     This case involves two payments made to the French
government: Contribution Sociale Géneralisee (General
Social Contribution, abbreviated as CSG) and Contribution
pour le Remboursement de la Dette Sociale (Contribution for
the Repayment of Social Debt, abbreviated as CRDS). Both
were enacted after the Totalization Agreement went into
effect.



2
   The covered provisions of French law are: (i) “laws establishing
the administrative organization of social security programs”; (ii)
“laws establishing the social insurance system for nonagricultural
employees and laws establishing the social insurance system for
agricultural employees”; (iii) “laws on prevention and
compensation of occupational accidents and illnesses,” and “laws
on nonoccupational accident insurance and insurance against
occupational accidents and illnesses for self-employed persons in
agricultural occupations”; (iv) “laws on family benefits”; (v) “laws
concerning special social security systems to the extent they relate
to the risks or benefits covered by the laws enumerated in the
preceding clauses, but excluding the special system for civil
servants”; (vi) “the law on the system for seamen”; (vii) “laws
concerning sickness and maternity insurance for nonagricultural
self-employed workers and laws concerning sickness and maternity
insurance for agricultural self-employed workers”; and (viii) “laws
concerning old-age allowances and old-age insurance for
nonagricultural self-employed workers, laws concerning old-age
and invalidity insurance for clergymen and members of religious
orders, laws concerning old-age and invalidity insurance for
attorneys, and laws concerning old-age insurance for agricultural
self-employed workers.” Totalization Agreement, Art. 2(1)(b).
                              7
     The CSG law was enacted in December 1990. It is
codified in the Code de la Sécurité Sociale (Social Security
Code), which is not an enumerated French law in Article
Section 2(1)(b) of the Totalization Agreement, but includes
most provisions governing social security benefits in France.
CSG on employment income is withheld by the employer in
the same manner as other social security taxes and appears on
the employee’s pay stub as a social contribution. Employers
remit CSG directly to the Unions de Recouvrement des
Cotisations de Sécurité Sociale et d’Allocations Familiales
(Union for the Recovery of Social Security and Family
Allowances Premiums). The Union is a network of private
organizations, the main task of which is to collect the
employee and employer social security contributions that
finance France’s social security system.

     CSG revenues are allocated to five separate funds within
the French government: the National Family Allowances
Fund, compulsory health schemes, the Old-Age Solidarity
Fund, the National Solidarity Fund for Autonomy for the
elderly and disabled, and the Social Debt Redemption Fund.
The Social Debt Redemption Fund is dedicated primarily to
the retirement of debt incurred to fund French social security
programs in the 1990s, but it also appears to finance certain
payments made to France’s general budget. The percentage
of CSG devoted to the National Solidarity Fund and the
Social Debt Redemption Fund is variable.

    The CRDS law was enacted in January 1996 and is not
codified. CRDS is withheld and collected in the same manner
as CSG. CRDS proceeds go to the Social Debt Redemption
Fund.

    In 2001, the French government amended the social
security code to provide that CSG and CRDS are payable only
                               8
by individuals who are covered by a compulsory French
sickness insurance scheme. However, a 2012 amendment
made CSG and CRDS also applicable to gains realized on the
sale of French real property by non-French residents.

                               C

     Ory and Linda Coryell Eshel are married and are dual
citizens of the United States and France. In 2008 and 2009,
they resided in France, and Mr. Eshel earned a salary for
services performed in France. The Eshels paid various French
taxes, including CSG, CRDS, and French income,
unemployment, and social security taxes. Because Mr. Eshel
worked for a non-American employer, he was not required to
pay social security taxes to the United States.

     As United States citizens, the Eshels were liable for
United States income taxes for 2008 and 2009. They timely
filed federal income tax returns for both years, claiming
credits for French income tax, French unemployment tax,
CSG, and CRDS. The CSG and CRDS credits amounted to
$19,061 for 2008 and $32,672 for 2009.

     The Internal Revenue Service initially denied the entire
foreign tax credit for both years, but later conceded that all of
the claimed credits were valid except for CSG and CRDS.
The Eshels timely petitioned the tax court for redetermination
of the deficiencies. The parties also filed cross-motions for
summary judgment on the issue of whether CSG and CRDS
are foreign taxes that can be credited against tax liability.

     The tax court granted summary judgment for the
Commissioner. Because both CSG and CRDS were adopted
after the Totalization Agreement went into effect, the tax
court agreed with both parties that the central question was
                              9
whether the laws adopting those two taxes “amend or
supplement” the French laws enumerated in Article 2(1)(b) of
the Totalization Agreement. To answer that question, the tax
court turned to four American dictionaries to define “amend”
and “supplement,” and on the basis of those definitions
concluded that the phrase should mean “(1) formally altering
one or more of these laws by striking out, inserting, or
substituting words; (2) adding something to make up for a
lack or deficiency in one or more of these laws; or (3) adding
something to extend or strengthen the French social security
system as a whole.” J.A. 143 (citing Webster’s New World
College Dictionary (4th ed. 2010); Black’s Law Dictionary
(9th ed. 2009); American Heritage Dictionary (4th ed. 2000);
Webster’s New World Dictionary (2d coll. ed. 1980)).

     Relying on its dictionary definitions, the tax court
reasoned that CSG and CRDS “amend or supplement” the
designated French laws as long as they “add[] something to
extend or strengthen the French social security system as a
whole.” J.A. 143. The tax court also noted that both taxes are
administered by French social security officials and are
collected in the same manner as French social security taxes.
The court then determined that CSG “amends” the French
social security laws because it adds words to the Code de la
Sécurité Sociale, where most French social security laws are
codified. Id. at 149. The tax court also decided that CSG and
CRDS “supplement” the French social security laws because
they fund some benefits under laws identified in Article 2 and
discharge debt previously incurred to pay social security
benefits. Id. at 149–150.

    The tax court accordingly ruled that, because CSG and
CRDS “amend or supplement” the French social security laws
specified in the Totalization Agreement, they qualify as
payments made “in accordance with” the Totalization
                              10
Agreement and cannot be credited against United States
income tax liability. J.A. 124; 26 U.S.C. § 1401 note.

                              II

     We review de novo the tax court’s grant of summary
judgment, and can affirm only if there is no genuine dispute
as to any material fact and the Commissioner is entitled to
judgment as a matter of law.           See, e.g., Byers v.
Commissioner, 740 F.3d 668, 675 (D.C. Cir. 2014) (citing
Fed. R. Civ. P. 56(a)).

                              A

     The issue in this case is whether CSG and CRDS
“amend[] or supplement[]” the French laws enumerated in
Article 2(1)(b), within the meaning of the Totalization
Agreement. If they do, they are covered by the Totalization
Agreement and the Eshels may not claim them as a credit on
their United States tax returns. If they do not, they fall
outside of the Agreement, and the Eshels may credit them
against their United States income tax liability.

     The tax court’s conclusion that CSG and CRDS “amend[]
or supplement[]” the designated French laws was the product
of asking the wrong legal question. Rather than looking to the
text of the Totalization Agreement or the signatory countries’
shared understanding, the tax court asked only what “amends
or supplements” means in domestic dictionaries, as it might
do if construing a purely domestic statute.

      But the Totalization Agreement is not a domestic statute.
It is an executive agreement with a foreign country: initiated
by the State Department, negotiated by the Social Security
Administration, signed by the President and a foreign
                                11
government, and effective only after submission to Congress.
See Allison Christians, Taxing the Global Worker: Three
Spheres of International Social Security Coordination, 26 VA.
TAX REV. 81, 90–91 (2006). Executive agreements must be
interpreted under the same principles applicable to
international treaties. See Air Canada v. United States Dep’t
of Transportation, 843 F.2d 1483, 1486 (D.C. Cir. 1988); see
also Kwan v. United States, 272 F.3d 1360, 1362 (Fed. Cir.
2001); Bank Melli Iran v. Pahlavi, 58 F.3d 1406, 1408 (9th
Cir. 1995).

     International executive agreements and treaties are
primarily “compact[s] between independent nations,” Lozano
v. Montoya Alvarez, 134 S. Ct. 1224, 1232 (2014) (quoting
Medellín v. Texas, 552 U.S. 491, 505 (2008)), and it is “our
responsibility to read [them] in a manner ‘consistent with the
shared expectations of the contracting parties,’” Lozano, 134
S. Ct. at 1232 (emphasis in original) (quoting Olympic
Airways v. Husain, 540 U.S. 644, 650 (2004)). Our goal is
“to ascertain the intent of the parties by looking to the
document’s text and context.” Lozano, 134 S. Ct. at 1232
(quoting United States v. Choctaw Nation, 179 U.S. 494, 535
(1900)). To that end, it is inappropriate to make the United
States’ maxims for statutory construction unilaterally
dispositive. “Even if a background principle is relevant to the
interpretation of federal statutes, it has no proper role in the
interpretation of treaties unless that principle is shared by the
parties to ‘an agreement among sovereign powers.’” Lozano,
134 S. Ct. at 1232 (quoting Zicherman v. Korean Air Lines
Co., 516 U.S. 217, 226 (1996)).

     Instead, the tax court should have started with the
Totalization Agreement’s plain text. “The interpretation of a
treaty, like the interpretation of a statute, begins with its text.”
Medellín, 552 U.S. at 506. The text of a treaty or executive
                              12
agreement controls “unless ‘application of the words of the
treaty according to their obvious meaning effects a result
inconsistent with the intent or expectations of its
signatories.’” United States v. Stuart, 489 U.S. 353, 365–366
(1989) (quoting Sumitomo Shoji America v. Avagliano, 457
U.S. 176, 180 (1982)).

     Here, the Agreement’s text provides powerful evidence
of its meaning. Article 1 defines certain terms in the
Agreement, but does not define “amends or supplements.”
For those undefined terms, Article 1 directs that “[a]ny term
not defined in this Article shall have the meaning assigned to
it in the laws which are being applied.” Totalization
Agreement, Art. 1(10). The Agreement defines “laws,” in
turn, as “the laws and regulations specified in Article 2.” Id.
Art. 1(3). Those Article 2 laws are the laws covered by the
Agreement: the eight enumerated types of French laws, two
United States laws, and “legislation which amends or
supplements the laws specified[.]” Id. Art. 2(3). Thus,
whether CSG and CRDS “amend[] or supplement[]” the
enumerated French laws is fundamentally an inquiry into the
content and meaning of the Article 2 laws—in this case, the
Article 2(b) French laws. For that reason, determining the
“meaning” of “amend[ing] or supplement[ing]” the French
laws should have at least in part been informed by French
law.

     The problems with the tax court’s approach do not stop
there. The tax court also improperly divorced “amends or
supplements” from its textual object. Rather than asking
whether CSG and CRDS amend or supplement “the laws
specified” in Article 2(1)(b), the tax court considered whether
CSG and CRDS amend or supplement the “French social
security system as a whole.” J.A. 143 (emphasis added). The
court erroneously relied on the relationship between CSG and
                              13
CRDS and the French social security program generally,
noting only that revenues from the taxes were allocated in
some (unknown) part to social security schemes and debt
incurred by social security programs. In short, the plain text
of the Totalization Agreement forecloses the definition the
court applied, which looked not to “the laws specified,”
Article 2(3), but the French social security system as a whole.

     Finally, at oral argument, the Commissioner admitted not
knowing what one of the recipients of CSG taxes—the
National Solidarity Fund for Autonomy—“actually funds.”
Oral Arg. Tr. 36. But the Commissioner “submit[ted] that
that’s immaterial because,” as long as a levy supplements
some “categories of laws that are included in the Treaty, the
fact that some portion of the revenue is directed elsewhere
does not mitigate th[e] conclusion” and the entire tax is
deemed subject to the Totalization Agreement. Id. at 36.
Indeed, in the Commissioner’s view, the CSG and CRDS
would “amend[] or supplement[]” the French laws in the
Totalization Agreement if even a single Euro of their
proceeds funded any law included in the Agreement. Id. at
48–49 (Q: “Your view of this agreement * * * is that if it
were even de minimis one Euro it would count as
‘supplement’?” A: “Based on the way that * * * the
agreement is drawn, yes.”).

    That extreme reading of the Totalization Agreement rests
on nothing more than the Commissioner’s own say-so. It
lacks any grounding in the Agreement’s text or in any
principle governing the interpretation of international
agreements. The tax court’s corresponding disregard of the
Totalization Agreement’s textual direction concerning the role
of French law in resolving undefined terms and in
determining the content of the laws enumerated in Article
2(1)(b) was error and requires reversal.
                              14

                               B

     To the extent that ambiguity remains about the status of
CSG and CRDS and their relationship to the identified French
laws, the tax court should have consulted sources illuminating
the “shared expectations of the contracting parties,” such as
“the negotiating and drafting history” and “the postratification
understanding of the contracting parties.” Zicherman, 516
U.S. at 223. Additionally, “[a]lthough not conclusive, the
meaning attributed to treaty provisions by the Government
agencies charged with their negotiation and enforcement is
entitled to great weight.” Sumitomo, 457 U.S. at 184–185; see
also Kolovrat v. Oregon, 366 U.S. 187, 194 (1961).

     For instance, in Kolovrat, the Supreme Court held that a
treaty between the United States and Serbia trumped a state
statute that would have limited the ability of aliens to inherit
property. 366 U.S. at 188–189. In so holding, the Supreme
Court relied upon “diplomatic notes exchanged between the
responsible agencies of the United States and of Yugoslavia”
to guide its determination of the agreement’s meaning. Id. at
194.

     Likewise, in Sumitomo, the Court analyzed whether
Sumitomo was a company of Japan under the Friendship,
Commerce, and Navigation Treaty between the United States
and Japan. 457 U.S. at 179. As evidence of the Japanese
position, the Court looked to a cable from the Japanese
Ministry of Foreign Affairs to the Secretary of State,
explicitly stating that a company in Sumitomo’s position was
not covered by the relevant provision of the treaty. Id. at 184.
As evidence of the federal government’s position, the Court
looked to the brief for the United States as amicus curiae,
                             15
which communicated the State Department’s position and
conformed with Japan’s view. Id. at 184 n.10.

     The tax court failed to follow that direction, relying
instead on nontextual sources that did not purport to
communicate the countries’ official positions or shared
expectations.

     The Commissioner argues that the United States
government has consistently regarded CSG and CRDS as
covered by the Totalization Agreement. But he builds that
argument with the wrong tools. He relies on only a
declaration of an individual in the Social Security
Administration and a 1997 letter from the United States
embassy, neither of which purports to offer an authoritative
statement of the view of the United States as a party to the
Totalization Agreement, let alone to reflect the shared
understanding of both signatory governments.

      The declaration on which the Commissioner relied is by
Vance Teel, the Associate Commissioner of the Office of
International Programs of the Social Security Administration.
In it, Teel states: “Based on information available to me and
to the best of my understanding and belief,” CSG and CRDS
are covered by the Totalization Agreement. J.A. 60–61. That
is it. Teel provides no explanation about what information
was available to him, nor does he identify the source of his
understanding and belief. More to the point, the government
conceded that the declaration “is not establishing an official
state position of the United States of America” as a party to
the Totalization Agreement, Oral Arg. Tr. 26, nor does it
purport to document a settled understanding of the taxes’
status.
                               16
     The 1997 letter is equally insufficient. The letter is from
Donald Bandler, the interim head of the United States
embassy in France at that time, and is addressed to the French
Minister of Social Affairs and Employment. The letter
discusses the tax treatment of United States “detached”
workers in France—that is, United States citizens working in
France for a United States employer for a period of less than
five years. J.A. 120; see Totalization Agreement, Art. 6(1).
Detached workers are covered only by the tax laws and the
social security system of the United States. Unlike the Eshels,
they do not make payments into the French social security
system. Totalization Agreement, Art. 6(1). In the letter,
Bandler challenges the imposition of CSG and CRDS on
detached workers and urges the French Minister to change his
policy to treat CSG and CRDS as covered by the Totalization
Agreement, and thereby inapplicable to United States
detached workers.

     But that just shows that, at that time, the French
government was imposing CSG and CRDS on United States
detached workers. The letter thus suggests that the French
government considered the taxes to be outside of the
Totalization Agreement, and thus at most might indicate a
conflict between the French and American positions, not a
shared understanding. But it cannot even do that because the
letter’s author asserted no authority to speak for the State
Department or the United States government as a party to the
Agreement. Nor did counsel claim that the letter had any
such weight. To the contrary, counsel for the Commissioner
again admitted at oral argument that “nothing I say here is a
pronouncement on the position of the United States in any
matters related to foreign relations.” Oral Arg. Tr. 24. 3

3
 In 2001, the French government passed legislation that ended the
imposition of CSG and CRDS on United States detached workers.
                               17

     The Commissioner’s position, moreover, is the legal
equivalent of trying to clap with one hand. The question of
whether CSG and CRDS amend or supplement the French
laws in the Totalization Agreement turns on the shared
expectations of both the United States and French
governments, which are grounded in the provisions of the
Agreement that address the role of French law in discerning
the amended or supplemented content of the French laws
enumerated in Article 2(b). See Totalization Agreement, Art.
1(10).

     The Eshels, for their part, relied principally on three
statements of the French government: a 1999 statement by
the French Finance Minister in answer to a parliamentary
question, a French “Statement of Practice” from 1998, and a
statement of the French Minister of Foreign Affairs in May
2007. See J.A. 24, 25, 70. The Eshels also provided the
expert report of Philippe Derouin, a Paris tax lawyer. See id.
at 94–113.

    The Eshels, however, offer little to no context for those
assorted ministerial statements, and the record contains only
excerpts of each. At this juncture, the Eshels provide no
sound basis for this court to conclude as a matter of law that
the statements represent the view of the French government
on either the proper interpretation of the Totalization
Agreement or on whether CSG and CRDS amend,




If CSG and CRDS had actually amended or supplemented the
designated French laws, the taxes would have fallen within the
Totalization Agreement, raising a question as to the need for such
independent legislation.
                                18
supplement, or have any other legal relationship to the French
laws specified in the Totalization Agreement. 4

     Moreover, the Eshels’ evidence primarily speaks to
whether CSG and CRDS are covered by the French Income
Tax Treaty, which coordinates the French and American
assessment of income tax realized by residents of the foreign
counterparty on domestic sources. At oral argument, the
Eshels explained that the Income Tax Treaty and the
Totalization Agreement are mutually exclusive: they cannot
cover the same tax “if they give you different answers.” Oral
Arg. Tr. 18. That argument certainly remains open to be
explored on remand, but at this procedural juncture and on
this limited record, it cannot be conclusive. Indeed, the
Eshels’ own expert acknowledged that there is “no judicial or
administrative precedent in France expressly addressing the
question whether CSG and CRDS are covered by the U.S.-
France Totalization Agreement.” J.A. 94.

                                C

     The central problem in this case is that the tax court’s
resort to American dictionary definitions pretermitted the
critical inquiry into the Agreement’s text and the signatory
countries’ shared understanding of the Agreement. The text
strongly suggests that the question whether CSG and CRDS
amend or supplement the designated French laws—which is
fundamentally an inquiry into the content and meaning of the
textually enumerated French laws—should have involved
reference to French law. Instead of heeding this instruction,
4
 At oral argument, the Eshels represented that those ministers are
overseen by the French liaison agencies identified in the
Administrative Arrangement—the Center for Social Security of
Migrant Workers and the National Independent Social Security
Fund for Miners—but nothing in the record substantiates that point.
                                  19
the tax court consulted outside sources that were not reliable
expressions of either textual construction or the signatories’
intent.

     In short-circuiting those inquiries, the tax court invoked
Tax Court Rule 146, which provides that a dispute over
foreign law is a legal, not a factual, dispute. We have no
disagreement with that point. See Fed. R. Civ. P. 44.1 (“In
determining foreign law * * * [t]he court’s determination
must be treated as a ruling on a question of law.”); see also
McKesson Corp. v. Islamic Republic of Iran, 753 F.3d 239,
242 (D.C. Cir. 2014) (This court “review[s] de novo * * * the
district court’s interpretation of foreign law.”).

     Where the tax court went astray was in the sources of
legal authority on which it relied. In resolving difficult
questions of foreign law and in attempting to ascertain the
views of a foreign government on an agreement to which it is
a party, courts are empowered to “insist on a complete
presentation by counsel.” Fed. R. Civ. P. 44.1 Advisory
Committee Notes 1966. If the litigants’ submissions come up
short, the court may choose to “request a further showing by
counsel, or engage in its own research, or direct that a hearing
be held, with or without oral testimony, to resolve the issue.”
Charles Alan Wright & Arthur R. Miller, Federal Practice &
Procedure, § 2444 Proof of Foreign Law (3d ed. 1998). 5
Courts may also request amicus submissions from the United
States providing its official position on the interpretation of an
agreement with a foreign government, and can ask the State
Department to provide the views of the foreign government.
5
  Those principles for district court litigation apply with equal force
to this type of tax court determination. Cf. Byers, 740 F.3d at 675
(“We review decisions of the Tax Court ‘in the same manner and to
the same extent as decisions of the district courts in civil actions
tried without a jury.’”) (quoting 26 U.S.C. § 7482(a)(1)).
                              20

    When, as here, the trial court failed to inquire properly
into the meaning of an international agreement, remand is
appropriate. See Tobar v. United States, 639 F.3d 1191, 1200
(9th Cir. 2011) (“[T]he district court apparently did not
recognize that, in its discretion, it could inquire further into
the content of Ecuadorian law.”); cf. Railway Labor
Executives’ Ass’n v. United States Railroad Retirement Bd.,
749 F.2d 856, 864 (D.C. Cir. 1984) (remanding to the
Railroad Retirement Board because the Board did not
coherently articulate why Canadian immigration regulations
were covered by the relevant United States statutes).

                              III

    The Totalization Agreement is an international executive
agreement that must be interpreted in light of its full text and
the shared expectations of the contracting governments.
Because the tax court committed legal error in its analysis of
those questions, we reverse the judgment of the tax court and
remand for further proceedings consistent with this opinion.

                                                    So ordered.
