*1158Opinion by Chief Judge KOZINSKI; Partial Concurrence and Partial Dissent by Judge BYBEE.
ORDER
The opinion is amended to replace the first two sentences of the first full paragraph on page 11321 of the slip opinion with the following:
< Although the evidence under count 2 would have been sufficient to support the jury’s verdict, had the jury been properly instructed, it was ambiguous. Officer Kirby testified that she would not have ordered her dog to attack “without [Harrison] saying that he was going to do something to me,” but she also said she was “not a hundred percent confident that he said he was going to attack me.” And while at times Officer Kirby said that Harrison “started running” in her direction, at other times she said he merely “looked like he was starting to come running.’^
Appellant’s Petition for Rehearing and for Rehearing En Banc is otherwise denied. See Fed. R.App. P. 35, 40. Judge Bybee would grant the petition.
No further petitions for rehearing or rehearing en banc may be filed.
KOZINSKI, Chief Judge:Everyone could have done more to protect defendant’s rights at trial.
I
This is a tale of two Rex Harrisons. The first is the Harrison of Officers Jenkins and Kirby, two military police officers, who describe a man so drunk he could barely stand straight. A man who reeked of alcohol at a distance of six feet. Who snarled, “I don’t think I should have to give you shit” when asked for his driver’s license. A man who punched Officer Jenkins in the face and told Officer Kirby, “I’m not afraid of you and I’m not afraid of your fucking dog.”
The second Rex Harrison is the man of his own telling. This Harrison had only “a couple of beers with dinner.” When confronted by the officers, he humbly apologized for trespassing. This Harrison was calm and non-confrontational; he had the milk of human kindness by the quart in every vein. He certainly never hit anyone.
The jury must have believed the first story because it convicted Harrison of two counts of assaulting a federal officer. He appeals.
II
Except where otherwise noted, Harrison’s trial lawyer failed to object to the errors his new lawyer raises on appeal. We therefore review for plain error, asking the usual questions, including whether there was prejudice. See, e.g., United States v. Recio, 371 F.3d 1093, 1100 (9th Cir.2004).
Count 1
A. Harrison was convicted of assaulting Officer Jenkins and inflicting “bodily injury.” 18 U.S.C. § 111(b). He complains that the prosecutors engaged in improper questioning during cross-examination and improper “vouching” during closing arguments.
It’s black letter law that a prosecutor may not ask a defendant to comment on the truthfulness of another witness, United States v. Combs, 379 F.3d 564, 572 (9th Cir.2004), United States v. Geston, 299 F.3d, 1130, 1136 (9th Cir.2002), but the prosecutors here did just that. One prosecutor asked: “You’re saying that [they’re] going on the stand, swearing an oath to testify to the truth and then lying ... ?” *1159He even pitted his own credibility against Harrison’s, asking, “So I’m in the conspiracy against you, is that right?” These were not isolated incidents: Improper questioning was an organizational theme for the prosecutor’s entire cross-examination.
The vouching was similarly 'patent. The government was entitled to rebut Harrison’s suggestion that Officers Jenkins and Kirby were motivated to lie, but it crossed the line when one prosecutor mentioned during closing that the officers had been promoted “with no adverse action whatsoever” after an internal military investigation. This clearly “suggest[ed] that information not presented to the jury,” but available to the investigators, supported the officers’ testimony. United States v. Necoechea, 986 F.2d 1273, 1276 (9th Cir.1993). And it would be hard to find a clearer case of “placing the prestige of the government behind a witness,” id., than the prosecutor’s statement that the “[government stands behind” Officers Jenkins and Kirby.
The government concedes the impropriety of many of these statements, but points out that the prosecutors were Special Assistant United States Attorneys on loan from the military. That’s no excuse at all; when the United States Attorney endows lawyers with the powers of federal prosecutors, he has a responsibility to properly train and supervise them so as to avoid trampling defendants’ rights. Indeed, everyone involved could have done better: The defense attorney should have objected as soon as he saw the prosecutors step out of line. And the respected and experienced district judge should not have tolerated this protracted exhibition of unprofessional conduct.
Nevertheless, Harrison must also show prejudice, and he hasn’t. Harrison insists the government’s case was “not overwhelming, but consisted of no more than a credibility contest....” But the government presented physical evidence of Harrison’s guilt, including an injury to one of his knuckles. Harrison admitted making a spurious 911 stolen-car call when he knew full well his car was with the MPs. A state police officer who saw Harrison later that night testified to his extreme intoxication. And both the state police officer and a third MP testified that Harrison used profanity and struggled while being arrested. After four witnesses undermined Harrison’s credibility, we cannot say the prosecutors’ misconduct “affected the outcome of the district court proceedings.” United States v. Olano, 507 U.S. 725, 734, 113 S.Ct. 1770, 123 L.Ed.2d 508 (1993). Any prejudice from the vouching was also ameliorated by the judge’s belated curative instruction. See Combs, 379 F.3d at 575.
Harrison relies on Geston and Combs, but they are not on point. Combs reduced to a pure credibility contest between a defendant and two witnesses. 379 F.3d at 573. In Geston, because a prior trial resulted in a hung jury, we inferred that the case was a close one and thought the prosecutor’s misconduct might well have tipped the balance. 299 F.3d at 1136.
B. Harrison claims the jury should not have been instructed that it could infer consciousness of guilt from his flight. Such an instruction is proper only if the evidence supports “a chain of unbroken inferences” from (1) defendant’s behavior to flight; (2) flight to consciousness of guilt; (3) consciousness of guilt to consciousness of guilt concerning the crime charged; and (4) consciousness of guilt concerning the crime charged to actual guilt of the crime charged. United States v. Dixon, 201 F.3d 1223, 1232 (9th Cir.2000). Courts consider “whether the defendant knew the police suspected him of a *1160particular crime” and “whether the defendant fled immediately after the crime.” Id. Harrison objected at trial, so we review for abuse of discretion. United States v. Perkins, 937 F.2d 1397, 1401 (9th Cir.1991).
With respect to count 1, all the necessary inferences were supported. Having struck an officer in the face, Harrison would have been aware that police suspected him of a crime. And Harrison surely did flee the scene. Harrison claims the chain of inferences was broken when he reported his car as stolen. But the jury could have inferred that he made a false report in an effort to set up an imaginary car thief as the fall-guy for his crimes. Nor can we say the instruction was invalid because the jury might have mistakenly thought it applied to Harrison’s first attempt to run away, prior to striking Officer Jenkins. The instruction permitted the jury to draw a reasonable inference; it did not require an unreasonable one. No reasonable jury would have inferred that Harrison was conscious of guilt because he fled prior to committing the crime.
C. Harrison suggests that the multiple errors at trial deprived him of his due process and fair trial rights and urges us to reverse under a “cumulative effects” theory. But the errors did not render the trial “fundamentally unfair.” Parle v. Runnels, 505 F.3d 922, 927 (9th Cir.2007). The prosecutor’s improper questioning only highlighted a credibility judgment that Harrison was himself asking the jury to make. And the prosecutor’s vouching, when paired with a curative instruction, did not make the defense “far less persuasive than it might [otherwise] have been.” Id. (quoting Chambers v. Mississippi, 410 U.S. 284, 294, 93 S.Ct. 1038, 35 L.Ed.2d 297 (1973)).
Count 2
Harrison was also convicted of forcibly assaulting, resisting, opposing, impeding, intimidating, or interfering with Officer Kirby. 18 U.S.C. § 111(a). Harrison challenges his conviction based on the same prosecutorial misconduct and an additional erroneous jury instruction.
A. The misconduct once again was not prejudicial. To be sure, because there were no witnesses other than Harrison and Officer Kirby, this part of the case did reduce to a credibility contest akin to Geston or Combs. But once the jury believed that Harrison struck Officer Jenkins, it was not going to believe Harrison when he claimed he was a perfect gentleman towards Officer Kirby.
B. The district court told the jury it could convict if “the defendant intentionally used force in assaulting, resisting, or intimidating” Officer Kirby, and it clarified that “[t]here is use of force when one person intentionally physically ... intimidates ... another.” That was plain error. While “a defendant may be convicted of violating section 111 if he ... uses any force whatsoever against a federal officer,” including a mere threat of force, United States v. Sommerstedt, 752 F.2d 1494, 1496 (9th Cir.1985), the instruction here defined “force” out of the statute entirely by equating it with physical intimidation. As instructed, the jury could have convicted Harrison for no more than purposefully standing in a way that emphasized his size and strength. The instruction was likewise improper under United States v. Chapman, which clarified after Harrison’s trial that section 111 always requires proof of an assault. 528 F.3d 1215, 1222 (9th Cir.2008). Just as physical intimidation need not involve use of force, it will not always constitute assault.
*1161We cannot find the “strong and convincing evidence” of force or assault that might excuse this instruction under plain error review. See United States v. Alferahin, 433 F.3d 1148, 1158 (9th Cir.2006). The government suggests that the jury’s verdict on the third (state law) count of the indictment shows that it necessarily found the missing elements, but that count involved conduct at an entirely different time.
Although the evidence under count 2 would have been sufficient to support the jury’s verdict, had the jury been properly instructed, it was ambiguous. Officer Kirby testified that she would not have ordered her dog to attack “without [Harrison] saying that he was going to do something to me,” but she also said she was “not a hundred percent confident that he said he was going to attack me.” And while at times Officer Kirby said that Harrison “started running” in her direction, at other times she said he merely “looked like he was starting to come running.” Certainly the evidence did not compel a finding of “force” under Sommerstedt — much less “assault” under Chapman.
Because Harrison might not have been convicted absent error below, we reverse with respect to count 2. We need not decide whether the court erroneously instructed the jury that it could infer consciousness of guilt under count 2 from Harrison’s flight after his encounter with Officer Kirby.
Ill
Harrison also challenges the district court’s enhancement of his sentence for lying on the stand. We review for clear error, asking whether the district court could have found (1) that Harrison gave false testimony, (2) on a material matter, (3) with willful intent. United States v. Garro, 517 F.3d 1163, 1171 (9th Cir.2008). According to Harrison, the fact that he stuck to his story after trial shows that he “honestly, if somewhat delusively,” believed his own testimony. But, after observing Harrison’s demeanor, the district court concluded that he “concocted a fanciful story, and then in order to cover one lie, lied again and then lied again.” In light of the patent discrepancy between Harrison’s testimony, the physical evidence and the testimony of every other witness, we cannot say that was clear error.
* * *
We uphold the judgment of conviction with respect to count 1 and reverse with respect to count 2. We also vacate Harrison’s sentence. See United States v. Ruiz-Alvarez, 211 F.3d 1181, 1184 (9th Cir.2000). This partial affirmance does not condone what happened at trial. Rather, this mixed result suggests only that trials can sometimes serve justice despite strenuous efforts to the contrary.
AFFIRMED IN PART, REVERSED IN PART AND REMANDED.