                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                  No. 03-30127
                Plaintiff-Appellee,           D.C. No.
               v.
                                         CR-01-00122-RFC
JEREMIAH C. SCHONEBERG,                    ORDER AND
             Defendant-Appellant.           AMENDED
                                            OPINION

       Appeal from the United States District Court
               for the District of Montana
       Richard F. Cebull, District Judge, Presiding

                 Argued and Submitted
         February 13, 2004—Seattle, Washington

               Filed November 17, 2004
         Amended Opinion Filed January 27, 2005

   Before: Dorothy W. Nelson, Andrew J. Kleinfeld, and
            Raymond C. Fisher, Circuit Judges.

                Opinion by Judge Kleinfeld




                           1137
                UNITED STATES v. SCHONEBERG            1139


                        COUNSEL

Palmer A. Hoovestal, Hoovestal, Kakuk & Fanning, Helena,
Montana, for the appellant.

James E. Sykora, Assistant United States Attorney, Billings,
Montana, for the appellee.


                         ORDER

  The Opinion filed on November 17, 2004, and appearing at
388 F.3d 1275 (9th Cir. 2004), is amended as follows:
1140             UNITED STATES v. SCHONEBERG
1.   At page 1276, delete “Magistrate Judge” and replace it
     with the following:

     District Judge

2.   At page 1280, at the end of the sentence beginning “Thus
     we are unable to,” add footnote 13 and the following
     footnote text:

     Though the parties did not cite United States v. Rud-
     berg, 122 F.3d 1199 (9th Cir. 1997), and United
     States v. Monroe, 943 F.2d 1007 (9th Cir. 1991),
     some interest has arisen within the court about
     whether this decision may be in tension with them.
     It is not. They are vouching cases, this is a Confron-
     tation Clause case. The Confrontation Clause confers
     a right upon “the accused.” U.S. CONST. amend.
     VI. The rule against vouching restricts conduct of a
     prosecutor, not the accused. Sometimes, as in Old
     Chief v. United States, 519 U.S. 172 (1996), or in the
     Sixth Amendment protection of the rights of “the
     accused,” there are asymmetries between what the
     prosecution and defense may do in a criminal trial.
     The prosecution’s use of the “truthful testimony”
     requirement of a plea bargain to bolster a prosecu-
     tion witness’s credibility may in some circumstances
     constitute impermissible vouching, as in Rudberg,
     and in some circumstances may not, as in Monroe,
     where the government introduced the “truthful testi-
     mony” aspects of the witness’s plea agreement only
     after the defendant had attacked the witness’s credi-
     bility. But the defense’s use of a witness’s plea
     agreement to attack a witness’s credibility obviously
     cannot violate the rule that “[t]he government may
     not vouch for the credibility of its witnesses by pre-
     senting the jury with personal assurances of the wit-
     ness’s veracity.” Monroe, 943 F.2d at 1013. We also
                   UNITED STATES v. SCHONEBERG                   1141
      note that the district court judge can limit a witness’s
      testimony or give cautionary instructions to the jury.

  In regard to the opinion filed on November 17, 2004, no
petition for rehearing was filed within the time required. Fed.
R. App. P. 40. With this amendment, no petitions for rehear-
ing or rehearing en banc shall be entertained.


                            OPINION

KLEINFELD, Circuit Judge:

  This is a Confrontation Clause case.

                               Facts

  Jeremiah Schoneberg was charged in an eleven-defendant
indictment for participating in a marijuana-distribution and
money-laundering conspiracy.1 But he was tried alone. Robert
Woodbury, the undisputed head of the group, had pled guilty
and been sentenced pursuant to a plea bargain to serve a little
under four years. In Schoneberg’s trial, Woodbury, another
conspirator who had also pled guilty pursuant to a plea bar-
gain, and Schoneberg’s ex-fiancée testified for the govern-
ment. Schoneberg testified on his own behalf.

   It was undisputed that when Woodbury, Schoneberg, and
the other defendants named in the indictment were in high
school together, Woodbury regularly sold marijuana to
Schoneberg, and Woodbury and Schoneberg were friends. In
high school, Schoneberg resold marijuana he had bought from
Woodbury, though the quantities were disputed. The high-
school dealing was long before the period of the conspiracy
charged in the indictment.
  1
   He was charged      under   21   U.S.C.   § 846   and   18   U.S.C.
§ 1956(a)(1)(A)(i).
1142             UNITED STATES v. SCHONEBERG
   After high school, the two remained friends, though they
were less close because Schoneberg lived in other places for
substantial periods. During the period of the alleged conspir-
acy, they were living in the same city and renewed their
friendship. The government witnesses’ accounts were basi-
cally that Woodbury, the head of the conspiracy, had deliv-
ered a pound of marijuana to Schoneberg, that Schoneberg
was selling it in smaller quantities, and that on three occa-
sions, Schoneberg wired money for Woodbury to give to
Woodbury’s dealer. Schoneberg’s account was basically that
Woodbury did indeed drop off a pound of marijuana at his
house and insinuated that he wanted Schoneberg to resell it
for him. But Schoneberg said he didn’t do that. Instead, he
and his then girlfriend (they got engaged later) smoked a little
less than half of the marijuana. When Woodbury came for the
money, they gave him back the marijuana that was left and
some cash that Schoneberg had saved. Later, when Woodbury
had someone threaten Schoneberg, Schoneberg’s girlfriend
wrote Woodbury a one-thousand-dollar check to cover the
rest.

   As for the money laundering, the indictment charged 31
transfers of money, three of them by Schoneberg. Wood-
bury’s method was to pay someone else $50 or so to buy a
money order at a grocery store and wire payment to a desig-
nated recipient. It was undisputed that Schoneberg wired
money for Woodbury three times. Woodbury testified that
Schoneberg knew he was wiring Woodbury’s payment for
Woodbury’s marijuana inventory. Schoneberg testified that he
was doing a favor for a friend and didn’t know who the recipi-
ent was or what the money was for, though by the third time
he was suspicious. Schoneberg’s ex-fiancée’s testimony
offered considerable support for both sides of the story,
though she testified for the government.

  The case turned on whether the jury believed Woodbury or
Schoneberg. The government had no audio or video tapes or
other evidence independent of what Woodbury (and to some
                  UNITED STATES v. SCHONEBERG                1143
extent Schoneberg’s ex-fiancée said. The jury could reason-
ably infer from Woodbury’s testimony that he recognized that
he had been caught and had obtained a plea bargain requiring
his cooperation, but had no more reason to lie since he had
already been sentenced. The jury could have reasonably
inferred that he was simply giving a truthful account of the
facts. A special twist was Woodbury’s testimony that his phy-
sicians had told him that he could expect to live less than his
sentence because of cystic fibrosis and he could expect to die
in prison. So it could have appeared to the jury that although
Woodbury held out hope of outliving his doctors’ expecta-
tions, he had nothing to gain from the government by lying.

    But Woodbury’s plea bargain reserved the possibility of a
sentence reduction after his testimony against his co-
conspirators. The government promised that if he provided
“substantial assistance,” the government would file a post-
sentencing motion to reduce his sentence pursuant to Federal
Rule of Criminal Procedure 35. As for whether he had pro-
vided “substantial assistance,” that determination was to be
“in the sole judgment of the United States Attorney’s Office.”
He was required to testify truthfully, of course, but “[n]othing
. . . limit[ed] the United States’ method of verifying” his truth-
fulness.

  Schoneberg’s attorney got Woodbury’s plea bargain into
evidence, but was not permitted to cross examine Woodbury
about whether his testimony was affected by the govern-
ment’s promise to move for a sentence reduction if his testi-
mony satisfied the government. The trouble started when
defense counsel asked Woodbury to confirm that under his
agreement, “the only party that is going to determine whether
you’re telling the truth today, as you’re standing on the wit-
ness stand, is the United States government, the United States
Attorney.” Woodbury answered, “I don’t know sir. I don’t
know how the law works.” Before defense counsel could
begin punching away at what was arguably an evasive and
misleading answer, the judge said, “What are you getting at?
1144             UNITED STATES v. SCHONEBERG
The jury decides whether he’s telling the truth.” Defense
counsel read Woodbury one of the paragraphs of his plea
agreement and asked him to confirm that it meant “[t]he
United States, those folks right there, a party to this lawsuit,
are the sole people that determine whether you’re telling the
truth or not.” Woodbury again claimed not to know “how the
law works,” and the prosecutor objected to defense counsel’s
question, saying “that’s a misrepresentation.” The judge
agreed, “[T]he jury in this case is the sole determiner of the
credibility of the witnesses in this case.” Defense counsel kept
trying, asking, “That means if they think that you’re telling
the truth and you’ve provided substantial assistance in the
prosecution of ---.” The prosecutor interrupted the question
with an objection, and the judge said, “Stop that, . . . I am not
going to tell you anymore. . . . I’m telling you not to talk
about that it’s the government’s obligation to determine the
truth, because it isn’t. It’s the jury’s determination in this
case.” Defense counsel was unsuccessful in persuading the
district judge that he was entitled to explore Woodbury’s
incentive to please the government. He did, however, get
Woodbury to admit he had a motive to testify against Schone-
berg in order to get his “Rule 35 motion.”

   The court recessed for the day as defense counsel strained
to get more into evidence. After the jury left, the court again
told counsel, “I don’t want you telling the jury that it’s the
government’s decision as to who is telling the truth in this
case.” Defense counsel again argued from the text of the plea
agreement, saying “Well, it kind of is.” But he was unsuccess-
ful.

  The jury convicted Schoneberg on both counts. He was
sentenced to serve 78 months of imprisonment (Woodbury
only got 42 months). He appeals.

                           Analysis

  As in many trials, the jury’s task boiled down to deciding
which of the two most important witnesses was lying to them.
                  UNITED STATES v. SCHONEBERG                   1145
The defendant had an obvious motive to lie, because his direct
freedom was at stake, but so did the government’s star wit-
ness. His motive was more subtle, as it arose from a plea
agreement that left open the possibility that he might walk out
the door a free man if the government was satisfied that his
testimony was the truth.

   The reason defense counsel, the court, and the prosecutor
were all talking past each other was that there were two trials
going on at the same time. For Schoneberg’s trial, the judge
was plainly correct that the jury was the sole judge of who
was telling the truth. But Woodbury was on trial too. The ver-
dict in his trial, however, would be a Rule 35 motion to
reduce his sentence for substantial assistance. This verdict
would be delivered by the United States Attorney’s Office,
and that office would be the sole judge of whether Woodbury
was telling the truth. Unless Woodbury were a man of the
highest “punctilio of . . . honor,”2 which would be surprising
for a dope dealer “rolling over” on his underlings, he would
be thinking at every moment that he testified whether the
Assistant United States Attorney would think that his testi-
mony was true. And since the Assistant United States Attor-
ney had no personal knowledge of the events, what he would
think was true might not actually be true. The prosecutor’s
objections, and the court’s rulings, prevented defense counsel
from cross examining Woodbury on the significance of his
testimony to this second “trial” that was taking place in the
shadows.

  [1] The Sixth Amendment right of the accused in a criminal
prosecution “to be confronted with the witnesses against him”3
guarantees him the right to cross examine those witnesses.4
The Supreme Court in Davis v. Alaska5 held that, even where
  2
    Meinhard v. Salmon, 164 N.E. 545, 546 (N.Y. 1928) (Cardozo, J.)
  3
    U.S. CONST. amend. VI.
  4
    Douglas v. Alabama, 380 U.S. 414, 418 (1965).
  5
    Davis v. Alaska, 415 U.S. 308 (1974).
1146               UNITED STATES v. SCHONEBERG
it offended a strong state policy of protecting confidentiality
of juvenile proceedings, a criminal defendant was entitled to
cross examine a witness about how his vulnerable status as a
probationer gave him a motivation to please the prosecutor.
Davis cannot be distinguished from the case at bar. The con-
stitutional right to cross examine is “[s]ubject always to the
broad discretion of a trial judge to preclude repetitive and
unduly harassing interrogation,”6 but that limitation cannot
preclude a defendant from asking, not only “whether [the wit-
ness] was biased” but also “to make a record from which to
argue why [the witness] might have been biased.”7
“[E]xposure of a witness’ motivation in testifying is a proper
and important function of the constitutionally protected right
of cross-examination.”8

   [2] Here, the jury got to see the presentence agreement term
regarding Rule 35 motions, but did not get to hear how this
term might have affected Woodbury’s motivation to satisfy
the Assistant United States Attorney. The court did not restrict
the inquiry to “preclude repetitive and unduly harassing inter-
rogation,” but rather on the erroneous ground that it was irrel-
evant and misleading, so we cannot sustain the limitation on
cross examination as an exercise of permissible discretion.
Schoneberg suffered a violation of his constitutional right of
confrontation. Where a plea agreement allows for some bene-
fit or detriment to flow to a witness as a result of his testi-
mony, the defendant must be permitted to cross examine the
witness sufficiently to make clear to the jury what benefit or
detriment will flow, and what will trigger the benefit or detri-
ment, to show why the witness might testify falsely in order
to gain the benefit or avoid the detriment.

  The government argues that we should sustain the district
  6
    Id. at 316.
  7
    Id. at 318 (emphasis added).
  8
    Id. at 316-17.
                     UNITED STATES v. SCHONEBERG                        1147
court’s exercise of discretion under United States v. Johnson,9
but that argument is misplaced because Johnson involved
whether the defendant could put on a separate expert witness,
not whether he could cross examine the witness whose credi-
bility was challenged. United States v. Jenkins10 does not save
the court’s exercise of discretion in this case either because in
Jenkins the court merely disallowed cross examination using
the conclusory phrase “coercion and duress” when voir dire
of the witness outside the presence of the jury established that
those words did not apply to the facts the witness described,
and the defense “was permitted to explore at length the pres-
sures” that the witness felt from the government.11

   [3] The government also argues that because our cases rou-
tinely say, as they must, that credibility of witnesses is solely
within the province of the jury,12 the cross examination would
have invaded the province of the jury. This argument is
unpersuasive. The credibility of witnesses in Schoneberg’s
trial was, of course, solely within the province of the jury, but
to evaluate that credibility, the jury was entitled to know what
motivation a witness might have to lie to them. Because a wit-
ness who is party to a forward-looking cooperation agree-
ment, with truthfulness to be determined by the government,
has a motivation to satisfy the government, the defendant is
entitled through cross examination to prove to the jury that the
witness has this incentive and that there may be reason to
question the witnesses’s credibility.

   More to the point, the government argues that Schoneberg
  9
    United States v. Johnson, 297 F.3d 845, 861-62 (9th Cir. 2002).
  10
      United States v. Jenkins, 884 F.2d 433 (9th Cir. 1989).
   11
      Id. at 437-438.
   12
      See, e.g., United States v. Geston, 299 F.3d 1130, 1136 (9th Cir. 2002)
(“ ‘It is the jurors’ responsibility to determine credibility by assessing the
witnesses and witness testimony in light of their own experience.’ ”)
(quoting United States v. Sanchez-Lima, 161 F.3d 545, 548 (9th Cir.
1998)).
1148                 UNITED STATES v. SCHONEBERG
was allowed to establish the terms of the plea agreement
regarding the Rule 35 motion and that he got Woodbury to
admit that he had a motive to testify against Schoneberg in
order to get this Rule 35 motion. That goes far toward satisfy-
ing the constitutional requirement. It does not go far enough
in this case, however, because counsel was not permitted to
cross examine Woodbury about how he could earn his Rule
35 motion: by satisfying the government that he was telling
the truth in his testimony against Schoneberg. Everyone in a
trial speaks to an audience, usually the jury, but the audience
that mattered to Woodbury’s fate was not the jury, it was the
prosecutor. Though arguably the predicate for Schoneberg’s
bias argument was sufficiently established by the words of
Woodbury’s plea agreement and his testimony showing that
he knew its terms, Schoneberg’s inquiry was cut off, and the
judge’s emphatic admonitions that the jury and not the prose-
cutor would judge whether Woodbury was telling the truth
vitiated the predicate that Schoneberg’s counsel had laid
down. Thus we are unable to place the ruling within the area
of permissible discretion.13
  13
     Though the parties did not cite United States v. Rudberg, 122 F.3d
1199 (9th Cir. 1997), and United States v. Monroe, 943 F.2d 1007 (9th
Cir. 1991), some interest has arisen within the court about whether this
decision may be in tension with them. It is not. They are vouching cases,
this is a Confrontation Clause case. The Confrontation Clause confers a
right upon “the accused.” U.S. CONST. amend. VI. The rule against
vouching restricts conduct of a prosecutor, not the accused. Sometimes, as
in Old Chief v. United States, 519 U.S. 172 (1996), or in the Sixth Amend-
ment protection of the rights of “the accused,” there are asymmetries
between what the prosecution and defense may do in a criminal trial. The
prosecution’s use of the “truthful testimony” requirement of a plea bargain
to bolster a prosecution witness’s credibility may in some circumstances
constitute impermissible vouching, as in Rudberg, and in some circum-
stances may not, as in Monroe, where the government introduced the
“truthful testimony” aspects of the witness’s plea agreement only after the
defendant had attacked the witness’s credibility. But the defense’s use of
a witness’s plea agreement to attack a witness’s credibility obviously can-
not violate the rule that “[t]he government may not vouch for the credibil-
ity of its witnesses by presenting the jury with personal assurances of the
witness’s veracity.” Monroe, 943 F.2d at 1013. We also note that the dis-
trict court judge can limit a witness’s testimony or give cautionary instruc-
tions to the jury.
                   UNITED STATES v. SCHONEBERG            1149
   Though constitutional error has been established, it is not
sufficient to compel a result. Under Delaware v. Van Arsdall,14
a confrontation clause violation does not result in automatic
reversal, but rather is “subject to the Chapman harmless-error
analysis.”15 The Supreme Court held in Van Arsdall that “[t]he
correct inquiry is whether, assuming that the damaging poten-
tial of the cross examination were fully realized,” we might
nevertheless say that the error was “harmless beyond a rea-
sonable doubt.”16 The importance of the testimony to the case,
presence or absence of other evidence corroborating or con-
tradicting the witness, extent of permitted cross-examination,
and overall strength of the prosecution’s case are among the
factors we consider in determining whether the error is harm-
less.17

   [4] We cannot conclude that the error was harmless here,
particularly because Schoneberg testified, and gave a logically
possible and not implausible account. It was plausible that, as
the government would have it, Schoneberg was plainly and
simply a marijuana dealer working for Woodbury. But
Schoneberg’s account is also plausible. He could have sold
small quantities of marijuana that Woodbury had sold him
some years before in high school, but not since. He could
merely have been an enthusiastic marijuana user who enjoyed
almost half of the pound of marijuana in his freezer with his
then girlfriend, but did not sell any. He could have given the
remainder back and paid for what he and his then girlfriend
had smoked when Woodbury and his heavy came around for
the proceeds. It was more of a stretch for Schoneberg to claim
that he was merely accommodating a friend on the money
transfers, and did not know that he was conducting financial
transactions with an intent to further a drug conspiracy. But
  14
     Delaware v. Van Arsdall, 475 U.S. 673 (1986).
  15
     Id. at 684.
  16
     Id.
  17
     Id.
1150            UNITED STATES v. SCHONEBERG
it would be too much to say that his account — that he sus-
pected the money was from marijuana but did not know, and
that his intent was merely to accommodate an old friend and
not to further a drug conspiracy — was false beyond a reason-
able doubt. The case turned on who was telling the truth,
Woodbury or Schoneberg, and the judge’s rulings and admo-
nitions left the jury completely understanding Schoneberg’s
motivation to lie, but not fully informed about Woodbury’s.

  REVERSED.
