Although President Trump confidently declared that he is willing to speak to special counsel Robert Mueller under oath, and is even “looking forward to it,” his principal lawyer advising him on the investigation, Ty Cobb, has darkly warned of a “perjury trap.” That “concern” has now been echoed by Trump supporters Roger Stone and Rush Limbaugh, who have both cautioned Trump about speaking with Mueller.

So, is Mueller really laying a trap for Trump? No. A “perjury trap” has a specific legal meaning as well as a broader, political one, but under neither understanding is Mueller’s request for an interview nefarious. This step is fully in line with Mueller’s investigative duties, and Trump will not be charged with perjury unless, well, he deliberately lies. The “perjury trap” talking point serves a completely different purpose: it represents the beginning of a political strategy to minimize and discredit any accusations that Mueller might ultimately lodge against Trump (most likely in the form of a report to the Deputy Attorney General or Congress).

As a pure legal matter, Cobb almost certainly knows that a “perjury trap” is an exceedingly narrow defense to a perjury charge that is completely inapplicable here. It comes into play only when prosecutors subpoena a person to the grand jury not for truly investigative reasons, but simply to try to get the person to commit perjury. A federal court explained the canonical view:

When testimony is elicited before a grand jury that is “attempting to obtain useful information in furtherance of its investigation,” United States v. Devitt, 499 F.2d 135, 140 (7th Cir. 1974) …, or “conducting a legitimate investigation into crimes which had in fact taken place within its jurisdiction,” United States v. Chevoor, 526 F.2d 185 (1st Cir. 1975) …, the perjury trap doctrine is, by definition, inapplicable.

That is the case here. There is no question that Trump has relevant information for the investigation, particularly since one focus of the inquiry is whether he himself committed obstruction of justice. (Of course, the President could choose to assert his Fifth Amendment privilege not to incriminate himself, but that is another matter.) Under these circumstances, Trump could never assert that he faced a “perjury trap” as a legal defense to any charge that he lied to Mueller or the grand jury.

No, something else is going on when Cobb and Trump’s supporters speak of a perjury trap. Initially, it should be said that their comments appear to reflect a (well-founded) fear that Trump will likely provide intentionally false testimony when questioned. In other words, he will trap himself. In fact, Cobb and Trump’s supporters may be aiming their comments about a “perjury trap” primarily at Trump himself, warning him through the television – apparently a great way to reach him – of the “trap” and that this time his lies could very well undo him. Obviously, the surest way for Trump to avoid a “perjury trap” is to simply tell the truth.

More broadly, it seems clear that the “perjury trap” talking point represents the beginning of what is essentially a political or public defense in the event Trump is eventually accused of perjury or obstruction of justice. The contention would be that the perjury charges are “unfair” or amount to an abuse of prosecutorial discretion. Although such a claim does not amount to a legal defense, strictly speaking, it could be part of a defense strategy even in a criminal case, with the aim of trying to poison the jury, judge and public against the prosecution. In the context of potential impeachment proceedings, which is an inherently political process, you can bet we would hear plenty about “perjury traps” and other similar accusations of prosecutorial wrongdoing.

But what is the accusation exactly? The “perjury trap” charge is actually used to describe three different kinds of complaints, relating to (1) the nature of the charge, (2) the reason a person might have lied, (3) whether perjury ends up being the only crime charged.

First, the term “perjury trap” is sometimes used to express an anxiety that prosecutors will turn good-faith mistakes in testimony, or honest failures to remember, into perjury charges. In The Terror Presidency, Jack Goldsmith wrote that when he received a grand jury subpoena in connection with a leak investigation, he worried about a “perjury trap”:

I of course had no intention of lying. But I could not remember many of the details of the hours of conversations I had with the FBI, and I feared that I might make statements under oath inconsistent with ones made in those conversations. (179-80).

Although the stress that grand jury witnesses sometimes feel is certainly real, the risk that prosecutors will charge innocent memory lapses as perjury is vastly overblown. Prosecutors know that perjury charges are exceedingly difficult to prove and that juries are sensitive to the possibility of honest forgetting or misremembering. Defendants (and their lawyers) will often claim that they forgot the truth (the Scooter Libby case comes to mind), but usually prosecutors will bring these cases only when there is overwhelming proof that the defendant intentionally lied about a material fact. Certainly in the case of Trump, it is hard to imagine perjury accusations being leveled on anything but clear evidence of lying about matters central to the investigation. But if Trump is accused of perjury, expect his lawyers and supporters to develop this line of attack and contend that Mueller is seeking to criminalize honest mistakes.

Second are instances when a person lies to investigators or a grand jury but does so for reasons that extend beyond trying to obstruct an investigation. Here the President Clinton case comes to mind. Clinton lied in response to questions about his sex life that some thought should never have been put to him and that were deeply personal and embarrassing. The same quandary arises when witnesses lie because they are genuinely afraid of the person they might implicate. In these cases, the “trap” is that the witness is caught between lying on the one hand and potentially causing themselves real harm on the other (harm that is above and beyond, or separate from, the ordinary pressures that witnesses might feel not to provide incriminating information). These cases are often the most difficult for prosecutors to assess. There is usually no question the person lied, but it’s rather a matter of whether the lie merits a criminal charge. Prosecutors will often reach very different judgments on these cases, depending on the particular circumstances and the consequences of the lie for the investigation. In any event, the risk of this problem occurring in the Trump interview is almost zero. If Trump lies, it will be because of the political costs of telling the truth or the criminal exposure that would result. These are not the kind of extenuating circumstances that anybody would think constitute “good” or “complicated” reasons for lying.

The third kind of case that gives rise to the accusation of a “perjury trap” is when nobody is indicted for the crime that was the subject of the investigation in the first place and therefore perjury ends up being the only crime charged. The perceived “unfairness” of this result is heightened when the person charged turns out to be a relatively low-level actor. For many, this was the central difficulty with the Scooter Libby case: in an investigation to determine who leaked the identity of a covert CIA officer, he was indicted for (and convicted of) lying even though the actual leaker was never charged. Along the same lines, we have already seen some describe the false statement crimes to which Michael Flynn and George Papadopoulos pled guilty as “mere process crime[s].”

If Trump is ultimately accused of perjury, and there are no charges arising from the collusion investigation, expect his lawyers and supporters to pursue a similar narrative. This strategy could also be deployed if Trump is accused of obstruction of justice, which raises distinct issues because it represents a more proactive interference with the investigation, but which is similarly separate and distinct from the allegations that are the object of the investigation. Trump’s lawyer and supporters will contend that the “trap” was the investigation in the first place, that prosecutors manufactured the criminality, that it is wrong to say that someone could obstruct an investigation that ended up bearing no fruit, and that it is unfair to bring perjury charges in a case where nobody is charged with substantive crimes.

Of course, these arguments are more difficult for the President of the United States to make than a low-level actor, but make them he and his surrogates will. If the accusations against him center only on obstruction of justice and/or perjury charges, he will likely say that it confirms his claim that the investigation was a witch hunt all along and that the accusations against him are the result of prosecutorial vindictiveness and abuse.

Some will continue to support Trump no matter what he says, but even some who do not back him might be sensitive to claims of prosecutorial overreaching when the main charges in an investigation are not pursued and the government brings only stand-alone obstruction or perjury charges. That would be a mistake. There are many reasons to be concerned about prosecutorial power and abuse, but this is not one of them. Not only is our system of justice dependent on witnesses telling the truth, and strong enforcement of this legal duty, but a robust ability to bring perjury and obstruction cases is particularly critical to the investigation of complex and difficult to detect crimes, such as organized crime, public corruption, and white-collar crime. These are the kinds of crimes we want prosecutors to focus on, but the reality is that without strong tools to pursue witnesses who intentionally lie or obstruct justice, the investigation of complex crimes will be severely undermined. By its very nature, complex crime is often difficult to detect and typically requires the truthful testimony of witnesses to expose it.

Defendants who are charged with “mere process crimes” will often contend that that prosecutors should focus on “real crime,” and will thereby seek to minimize or denigrate any charges of obstruction or perjury. The talk of a “perjury trap” by Trump’s lawyer and supporters suggests that they are already heading down this narrative path. Don’t be fooled. If Mueller accuses Trump of obstruction of justice or perjury, there will be no trap, unfairness, or overreaching. Just real crime.

(Alex Wong/Getty Images)