 United States Court of Appeals
          FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued March 3, 2017                    Decided May 16, 2017

                         No. 16-5232

  SENATE PERMANENT SUBCOMMITTEE ON INVESTIGATIONS,
                     APPELLEE

                               v.

                        CARL FERRER,
                         APPELLANT


                  Consolidated with 16-5274


        Appeals from the United States District Court
                for the District of Columbia
                    (No. 1:16-mc-00621)


    Robert Corn-Revere argued the cause for appellant. With
him on the briefs were Ronald G. London, Robert D. Luskin,
Stephen B. Kinnaird, Jamie S. Gardner, Steven R. Ross, and
Stanley M. Brand.

     Jessica Ring Amunson and Joshua M. Parker were on the
brief for amici curiae DKT Liberty Project, et al. in support of
appellant.
                               2
    Karen A. Chesley and David Boies were on the brief for
amici curiae Legal Momentum, et al. in support of appellee.

    Emma J. Llansó was on the brief for amici curiae Center
for Democracy & Technology and Electronic Frontier
Foundation in support of appellant.

     Thomas E. Caballero, Assistant Counsel, Office of Senate
Legal Counsel, argued the cause for appellee. With him on the
brief were Patricia Mack Bryan, Senate Legal Counsel,
Morgan J. Frankel, Deputy Senate Legal Counsel, and Grant
R. Vinik, Assistant Senate Legal Counsel.

    Before: TATEL, SRINIVASAN and WILKINS, Circuit Judges.

    Opinion for the Court filed by Circuit Judge TATEL.

     TATEL, Circuit Judge: Carl Ferrer, Chief Executive Officer
of the online advertising website Backpage.com, appeals two
district court orders directing him to produce various
documents in response to a subpoena issued by the Senate
Permanent Subcommittee on Investigations. During the
pendency of this appeal, however, Ferrer turned over some of
the documents, and the Subcommittee completed its
investigation and issued its final report. Given this, and given
that the Subcommittee no longer seeks to enforce the subpoena,
it argues that the case has become moot. Ferrer responds that
the case remains live because, according to him, this court can
order the Subcommittee to return, destroy, or refrain from
publishing the produced documents. We disagree. Because the
relief Ferrer seeks is barred by the separation of powers,
including the Speech or Debate Clause, the case is now moot.
                                3
                                I.

     In the first half of 2015, the Senate Permanent
Subcommittee on Investigations began examining “businesses
that directly or indirectly facilitate criminal sex trafficking
conduct, including trafficking in minors.” S. REP. NO. 114–
214, at 6 (2016). The Subcommittee suspected that online
advertisers were playing a central role in sex trafficking by
“providing . . . easily accessible forum[s] that match[] buyers
of sex with anonymous traffickers selling minors and adults.”
Id. at 3. In particular, the Subcommittee focused on
Backpage.com, a large, classified-advertising website that
allows third-party users to post their own ads. At that time,
Backpage featured, alongside run-of-the-mill categories like
real estate, jobs, and automobiles, a section dedicated to “adult”
services, which contained subcategories ranging from
“escorts” and “body rubs” to “adult jobs.” Subpoena Duces
Tecum of Oct. 1, 2015. Ads in those sections “typically
consist[ed] of a headline, a photo or photos, video, and a brief
description of the services being offered.” S. REP. NO. 114–
214, at 4.

     In April 2015, the Subcommittee asked Backpage for an
explanation of its “moderation” procedures, i.e., standards and
policies Backpage says it uses to “screen, block and remove
[user-supplied] ads . . . to guard against any form of human
trafficking or child exploitation.” Letter from Steven R. Ross,
Counsel to Backpage.com to Sens. Portman and McCaskill
(Oct. 23, 2015); see S. REP. NO. 114–214, at 7. Backpage sent
its General Counsel to be interviewed by the Subcommittee,
but when the Subcommittee found her answers lacking in
several respects, it sent follow-up questions and requests for
information, all of which went unanswered.
                               4
     On July 7, 2015, the Subcommittee issued its first
subpoena duces tecum asking Backpage to produce a variety of
documents. Responding through counsel, the company argued
that the subpoena was overbroad and a per se violation of the
First Amendment. Although the Subcommittee offered to
narrow the subpoena, Backpage continued insisting that the
subpoena violated the First Amendment.

     Seeking to end the stalemate, the Subcommittee withdrew
the initial subpoena on October 1 and then issued a new one to
Backpage’s CEO, Appellant Carl Ferrer. The new subpoena
sought eight categories of documents, giving Ferrer until
October 23 to respond or “assert any claim of privilege or other
right to withhold” documents in a privilege log. See Subpoena
Duces Tecum of Oct. 1, 2015.

     Although Ferrer supplied a handful of documents, he
refused to search for any other responsive material. He gave
three reasons for doing so: the subpoena exceeded the
Subcommittee’s investigative authority, infringed the First
Amendment rights of Backpage and its users, and sought
“[im]pertinent” information. Letter from Steven R. Ross to
Sens. Portman and McCaskill (Oct. 23, 2015).

    The Subcommittee rejected Ferrer’s objections, but
extended his deadline to comply until November 12. Ferrer
produced several more documents, repeated his three
objections, and added that he was withholding “[c]ertain
documents . . . on the basis of attorney-client and/or attorney
work product privilege.” Letter from Steven R. Ross to Sens.
Portman and McCaskill (Nov. 13, 2015).

    Confronted with Ferrer’s resistance, the Subcommittee
sought authority from the Senate to bring a civil subpoena-
enforcement action under 28 U.S.C. § 1365(a), which gives the
                                5
United States District Court for the District of Columbia
original jurisdiction “over any civil action brought by the
Senate or any authorized . . . subcommittee . . . to enforce . . .
any subp[o]ena or order issued by the Senate or . . .
subcommittee of the Senate to . . . any natural person.” With
the Senate’s unanimous approval, the Subcommittee filed an
enforcement application in district court. Ferrer responded with
the same three objections raised in his October 23 letter—that
the subpoena violated the First Amendment, pursued
impertinent materials, and exceeded the scope of the
Subcommittee’s investigative power.

    The District Court granted the Subcommittee’s application
on August 5, 2016, ordering Ferrer to comply with the
subpoena within ten days. Ferrer immediately noticed an
appeal and sought a stay in the district court, our court, and the
Supreme Court, all of which denied his request.

     On September 13, the day the Supreme Court denied a
stay, Ferrer produced some 110,000 pages of documents,
moved the district court for an extension to complete
production, and, for the first time in that court, invoked
attorney-client and work-product privileges as to a subset of the
yet-to-be produced documents. Although the district court
granted a short extension, it rejected as untimely Ferrer’s
assertion of privilege. Ferrer again appealed, and this court
denied a stay pending appeal except with respect to the
documents Ferrer claims are privileged.

     Ferrer turned over all concededly non-privileged
documents in late November. Some two months later, on
January 10, 2017, the Subcommittee held its last hearing,
issued a final report on sex trafficking (including a lengthy
appendix featuring certain documents Backpage produced),
and closed the investigation. Two weeks later, the
                                6
Subcommittee moved to dismiss this appeal, arguing that these
subsequent events had mooted the case and deprived this court
of jurisdiction.
                               II.

     Article III of the U.S. Constitution requires a controversy
to remain live “at all stages of review.” Decker v. Northwest
Environmental Defense Center, 133 S. Ct. 1326, 1335 (2013).
“For that reason, if an event occurs while a case is pending on
appeal that makes it impossible for the court to grant ‘any
effectual relief whatever’ to a prevailing party, the appeal must
be dismissed” as moot. Church of Scientology of California v.
United States, 506 U.S. 9, 12 (1992) (quoting Mills v. Green,
159 U.S. 651, 653 (1895)).

     The Subcommittee argues that the case has become moot
because the Subcommittee has “held its hearing, issued its final
report, . . . completed its investigation,” and “no longer seek[s]
to enforce any part of the subpoena.” Subcommittee Mot. to
Dismiss at 3, 12. Ferrer concedes that no controversy remains
as to the privileged documents he withheld, which the
Subcommittee has never received and no longer wants.
Subcommittee Mot. at 12; Oral Arg. Rec. 2:45–3:05.
Nonetheless, he insists, the dispute remains live because the
court may still provide at least some “effectual relief” by
ordering the Subcommittee to return, destroy, or refrain from
further publishing and distributing the documents Ferrer
produced. He also argues that even if the case has become
moot, the dispute satisfies the “capable of repetition yet
evading review” exception to mootness.
                               A.

    In support of his argument that this case remains live
because our court can order the Subcommittee to return or
                                7
destroy the documents, Ferrer relies principally on the Supreme
Court’s decision in Church of Scientology, 506 U.S. at 12. In
that case, the Internal Revenue Service issued an administrative
summons to a state-court clerk directing him to produce tape
recordings of conversations between officials of the Church of
Scientology and their attorneys. Id. at 10. When the IRS filed a
petition to enforce the summons in district court, the Church
intervened to oppose production on the grounds that the tapes
were privileged. Id. at 11. The district court ordered production
of the tapes and the Church appealed, but before the appeal
could be decided, the state-court clerk delivered the tapes to the
IRS, at which point the appellate court dismissed the case as
moot. Id. at 12. The Supreme Court reversed, explaining that
the controversy remained live because “a court . . . h[as] [the]
power to effectuate a partial remedy by ordering the
Government to destroy or return any and all copies it may have
in its possession.” Id. at 13.

     According to Ferrer, the same “destroy or return” remedy
is available here. We might agree were his documents held in
the grips of a federal agency. But as the Subcommittee points
out, because it is Congress that holds Ferrer’s documents, he
must contend with the cloak of protection afforded by the
Constitution’s separation of powers, including the Speech or
Debate Clause, which provides that, “for any Speech or Debate
in either House, [Members of Congress] shall not be questioned
in any other Place.” U.S. CONST. art. I, § 6, cl. 1.

     Although the Speech or Debate Clause chiefly functions to
immunize Members of Congress from civil or criminal liability
arising from “actions [falling] within the ‘legislative sphere,’”
Doe v. McMillan, 412 U.S. 306, 312 (1973), its protections
extend far more broadly. In Brown & Williamson Tobacco
Corp. v. Williams, 62 F.3d 408 (D.C. Cir. 1995), our court held
that the Clause affords Congress a “privilege to use materials
                                8
in its possession without judicial interference,” even where
unlawful acts facilitated their acquisition. Id. at 416. There, a
paralegal working for a law firm representing Brown &
Williamson stole internal tobacco-related documents and
arranged for their delivery to the House Subcommittee on
Health and the Environment. Id. at 411–12, 422. Suing the
paralegal for breach of contract in state court, the law firm
issued subpoenas to two Congressmen seeking production of
all documents in the Subcommittee’s possession. Id. at 412.
The Members removed the case to federal district court and
filed a motion to quash, arguing that the Speech or Debate
Clause barred the subpoena’s enforcement. Id. The district
court granted the motion, and our court affirmed, holding that
even though the documents had been stolen, “[a] party is no
more entitled to compel congressional testimony—or
production of documents—than it is to sue congressmen.” Id.
at 421. “[E]ven though material comes to a legislative
committee by means that are unlawful or otherwise subject to
judicial inquiry,” we explained, “the subsequent use of the
documents by the committee staff in the course of official
business is privileged legislative activity.” Id. at 417 (quoting
McSurley v. McClellan, 553 F.2d 1277, 1296–97 (D.C. Cir.
1976) (en banc) (per curiam)).

     In reaching its decision, Brown & Williamson relied in part
on Hearst v. Black, 87 F.2d 68 (D.C. Cir. 1936), in which our
court held that the separation of powers barred it from
enjoining a Senate committee from “keeping[,] . . . making any
use of[,] . . . or disclosing” the contents of telegraphs a Senate
committee had unlawfully obtained from the Washington
offices of publisher William Randolph Hearst. Id. at 71
(emphasis added). We explained then—and it is just as true
now—that “[w]e know of no case in which it has been held that
a court of equity has authority to do any of these things.” Id. To
circumscribe the committee’s use of material in its physical
                                9
possession would, we emphasized, “destroy[]” the
independence of the Legislature and “invade[]” the
constitutional separation of powers. Id. at 72; accord
McMillan, 412 U.S. 306, 338 n.11 (Blackmun, J., concurring
in part and dissenting in part) (“We have no more authority to
prevent Congress, or a committee . . . [,] from publishing a
document than to prevent them from publishing the
Congressional Record.”) (quoting Methodist Federation for
Social Action v. Eastland, 141 F. Supp. 729, 731 (D.D.C. 1956)
(three-judge court)); Sanders v. McClellan, 463 F.2d 894, 902
(D.C. Cir. 1972) (“The judiciary has the duty of not lightly
interfering with Congress’ exercise of its legitimate powers.”)
(internal quotation marks omitted).

     Brown & Williamson and Hearst thus make clear that the
separation of powers, including the Speech or Debate Clause,
bars this court from ordering a congressional committee to
return, destroy, or refrain from publishing the subpoenaed
documents. Because we can provide Ferrer with no “effectual
relief whatever,” Church of Scientology, 506 U.S. at 12, the
case has become moot.

     Resisting this conclusion, Ferrer first argues that because
the Subcommittee “enlist[ed] the jurisdiction of the judiciary”
under 28 U.S.C. § 1365, “it subject[ed] itself to that
jurisdiction,” meaning it “cannot . . . assert [that] separation of
powers precludes an adverse judicial resolution.” Appellant’s
Opp. to Appellee’s Mot. to Dismiss (“Opp. Br.”) at 10. We
disagree. Nothing in Section 1365—which gives the district
court “original jurisdiction . . . over any civil action brought by
the Senate or any authorized . . . subcommittee . . . to
enforce . . . any subp[o]ena”—provides that the Senate forfeits
its constitutional protections by seeking judicial enforcement
of a subpoena. Confirming this, the Senate Report
accompanying the statute’s enactment states that “[w]hen
                               10
Congress petitions the court in a subpoena enforcement action,
Congress does not waive its immunity from court interference
with its exercise of its constitutional powers.” S. REP. NO. 95–
170, at 94 (1977) (report accompanying Pub. L. No. 95–521,
92 Stat. 1824); see Mohamad v. Palestinian Authority, 556 U.S.
449, 459 (2012) (“[A]lthough we need not rely on legislative
history given the text’s clarity, we note that the history only
supports our interpretation . . . .”).

     Insofar as Ferrer contends that, apart from Section 1365’s
text, the Subcommittee necessarily accepted an implicit
restriction on the Speech or Debate Clause by seeking to enlist
the judiciary’s assistance in enforcing its subpoena, his
argument lacks merit. In ordering compliance with the
Subcommittee’s subpoena, the district court merely aided the
Senate in effectuating its inherent subpoena power. The
Subcommittee did not thereby necessarily invite the courts’
interference with constitutionally protected legislative activity.
Cf. United States v. Helstoski, 442 U.S. 477, 490–91 (1979)
(waiver of congressman’s Speech or Debate Clause immunity,
assuming such waiver is possible, would require “[a]n explicit
and unequivocal renunciation”).

     Citing two Supreme Court Speech or Debate Clause
cases—Hutchinson v. Proxmire, 443 U.S. 111 (1979), and
McMillan, 412 U.S. 306—Ferrer next argues that we may
prospectively enjoin the Subcommittee from further
disseminating Backpage’s documents “beyond the legitimate
legislative needs of Congress.” Opp. Br. 11. But Hutchinson
held only that the Speech or Debate Clause could not shield a
Senator from retrospective liability for defamatory statements
made in non-legislative publications. Hutchinson, 443 U.S. at
132–33. And McMillan concluded that the Clause barred an
award of damages and injunctive relief arising from a
congressional committee’s decision to publish materials whose
                               11
distribution was “otherwise actionable under local law,” at
least “insofar as [the complaint] sought relief from . . .
Committee members” and their legislative aides. McMillan,
412 U.S. at 312, 317. Neither case held that courts may
prospectively limit a congressional subcommittee’s lawful use
of documents in the course of a legitimate legislative activity.

     To be clear, we take no position on whether courts are
powerless to enjoin individual members—or the committees of
which they are a part—from disseminating investigative
materials whose contents have no relationship to legislative
functions or whose distribution would arguably violate the law.
See Watkins v. United States, 354 U.S. 178, 187 (1957)
(investigative activities “must be related to, and in furtherance
of, a legitimate task of the Congress”). That issue is not before
us. The Subcommittee obtained the documents in service of
legitimate legislative purposes and Ferrer makes no claim that
publishing them is “otherwise actionable” under any law.
                               B.

     This brings us to Ferrer’s alternative claim—that even if
the case has become moot, we may nonetheless entertain the
appeal under the exception to mootness for issues that are
“capable of repetition, yet evading review.” Spencer v. Kemna,
523 U.S. 1, 17 (1998). This exception applies where “(1) the
challenged action [is] in its duration too short to be fully
litigated prior to cessation or expiration, and (2) there [is] a
reasonable expectation that the same complaining party [will]
be subject to the same action again.” Id. (alterations in
original). We have no need to address the first requirement, for
Ferrer clearly fails the second.

     A controversy “is capable of repetition” only if “the same
parties will engage in litigation over the same issues in the
future.” Pharmachemie B.V. v. Barr Labs., Inc., 276 F.3d 627,
                                12
633 (D.C. Cir. 2002). “A ‘theoretical possibility,’ . . . is not
sufficient to qualify as ‘capable of repetition’[;] . . . . [t]here
must instead be a ‘reasonable expectation’ or ‘demonstrated
probability’ that the action will recur.” Beethoven.com LLC v.
Librarian of Congress, 394 F.3d 939, 951 (D.C. Cir. 2005)
(quoting Murphy v. Hunt, 455 U.S. 478, 482 (1982) (per
curiam)).

     According to Ferrer, “The threat that Backpage.com could
be compelled to produce documents intruding on its editorial
judgment in violation of the First Amendment is easily capable
of repetition.” Opp. Br. 15. For that to happen, however, Ferrer
would have to again have an enforcement action brought
against him for failing to comply with a similar subpoena,
seeking similar documents, and raising similar issues.
Although there is a “theoretical possibility” that this chain of
events might occur, Ferrer gives us no basis for believing that
there is a “reasonable expectation” or “demonstrated
probability” that it will. Murphy, 455 U.S. at 482; see
Pharmachemie, 276 F.3d at 633–34 (where “several
contingencies would have to occur for the same issues to arise
again,” party failed to “demonstrate[] a reasonable likelihood”
of repetition).

    Ferrer emphasizes that two members of the Subcommittee
have shown a continued interest in combating sex trafficking
on Backpage.com and on other forums. See Jan. 10, 2017
Hearing Before Senate Permanent Subcommittee on
Investigations, available at https://goo.gl/ot8PiM. Ranking
Minority Member McCaskill stated that she would “do
everything in [her] power to protect young women from being
exploited . . . on Backpage.com or anywhere else.” Id. 35:35–
36:05. And Chairman Portman reiterated that he was
“committed to continuing this effort, not just this one specific
goal of uncovering information that was not previously known
                                13
about Backpage . . . but a broader effort . . . looking at the laws
differently.” Id. 2:23:45–2:24:15. Such statements, however,
hardly establish a “reasonable expectation” that the
Subcommittee, having completed its work and issued its final
report, will nonetheless reopen its investigation and again issue
a subpoena to Ferrer.
                               III.

     Although Ferrer’s challenge to this subpoena-enforcement
order is moot, we emphasize that our decision does not leave
future subpoena recipients without a remedy. As counsel for
the Subcommittee pointed out at oral argument, “if you wish to
appeal an order . . . enforcing a Senate subpoena you stand on
your privilege, you go into contempt.” Oral Arg. Rec. 17:30–
45. For example, in In re Application of U.S. Senate Permanent
Subcommittee on Investigations (Cammisano), 655 F.2d 1232
(D.C. Cir. 1981), a district court enforced a Senate
subcommittee’s subpoena and, when the subpoena’s recipient
refused to comply, entered a separate order of civil contempt.
Id. at 1234–35. As a result, both the district court and this court
addressed his objections on the merits. Although the subpoena
recipient lost, through his disobedience he preserved his right
to appellate review of his objections. By contrast, Ferrer, by
responding to the subpoena, has triggered Congress’s
constitutional protections and thus deprived the courts of
authority “to grant any effectual relief whatever.” Church of
Scientology, 506 U.S. at 12.

    Finally, Ferrer asks that we vacate the district court’s
judgments if we dismiss the case as moot. “Courts usually”
exercise their equitable discretion to “vacate a judgment ‘when
mootness results from unilateral action of the party who
prevailed below’ or from circumstances beyond the control of
the parties.” Sands v. NLRB, 825 F.3d 778, 785 (D.C. Cir.
2016) (quoting U.S. Bancorp Mortgage Co. v. Bonner Mall
                               14
Partnership, 513 U.S. 18, 25 (1994)). That is exactly what
happened here. With respect to the documents Ferrer produced
over his First Amendment objection, any dispute was mooted
by operation of the Speech or Debate Clause. And with respect
to the documents Ferrer withheld pursuant to common law
privileges, the Subcommittee mooted the case by issuing its
final report and disclaiming any interest in further enforcing the
subpoena. Given this, and given that the Subcommittee itself
does not oppose vacatur, we vacate the district court’s
judgments and dismiss the case as moot. See Sands, 825 F.3d
at 786 (finding “opposing side’s silence” in the face of a party’s
request for vacatur to “significant[ly]” weigh in favor of
granting the request).

                                                     So ordered.
