Among the many questions surrounding Attorney General Jeff Sessions’s statements about his contact with Russian officials is whether the nation’s chief law enforcement official perjured himself in statements to members of the Senate. Two former federal prosecutors who spoke with The Washington Post indicated that proving such a case would be very, very difficult.

The facts at hand

For the full context of Sessions’s statements on Russia, see our timeline of the affair. For this discussion, two interactions are relevant.

On Jan. 10, Sessions answered a question from Sen. Al Franken (D-Minn.) under oath as part of his confirmation hearing to lead the Justice Department.

After roughly describing a CNN report about alleged ties between the campaign of Donald Trump and Russia, Franken asked if “there is any evidence that anyone affiliated with the Trump campaign communicated with the Russian government in the course of this campaign, what will you do?”

“Senator Franken, I’m not aware of any of those activities,” Sessions replied. “I have been called a surrogate at a time or two in that campaign, and I did not have communications with the Russians, and I’m unable to comment on it.”

On Jan. 17, Sen. Patrick J. Leahy (D-Vt.) asked additional questions of Sessions in a letter. Included among them: “Several of the President-Elect’s nominees or senior advisers have Russian ties. Have you been in contact with anyone connected to any part of the Russian government about the 2016 election, either before or after Election Day?”

Sessions replied, “No.”

On Wednesday, The Post reported that Sessions had twice met with Russian Ambassador Sergey Kislyak, once at an event and once in the senator’s office.

House Minority leader Nancy Pelosi says Attorney General Jeff Sessions "lied under oath" during his confirmation hearing and calls for his resignation (Reuters)

The statutes that apply

According to Jennifer Rodgers, a former federal prosecutor who now serves as the director of the Center for the Advancement of Public Integrity at Columbia Law School, two statutes apply to the questions above.

There’s 18 U.S. Code 1621, which describes the boundaries of the commission of perjury. In short, someone has committed perjury if he has taken an oath to tell the truth and then “states or subscribes any material matter which he does not believe to be true.” That he must believe the statement to be true is important; a mistake doesn’t count.

There’s also 18 U.S. Code 1001, which applies to the Leahy letter even if Sessions’s responses to the senator weren’t sworn. This statute prohibits falsifying or hiding information or providing materially false or fraudulent information to the government — even if not under oath. (It’s this statute, Rodgers notes, which was used to prosecute Martha Stewart.)

What the experts say

While the public perception of perjury is simply “lying under oath,” the experts we spoke with pointed out that the law is much more specific than that, which makes the question tricky.

“Could a gutsy prosecutor bring a case against the attorney general for perjury? Possibly,” said Paul Butler, a former federal prosecutor in the public integrity section of the Department of Justice who is now professor at Georgetown Law. “If you look at other perjury and false statement cases that the Justice Department has brought and state prosecutors have brought, I think you’d see cases that are less clear that prosecutors still bring.”

That said, Butler noted how difficult such a case would be. Perjury demands that the falsehood be material to the testimony, and in the response to Franken, Butler said he isn’t sure that Sessions’s statement about meeting with Russians was.

“He wasn’t asked directly about his own contacts, so he could say that his answer wasn’t material because that wasn’t really what the question was about,” Butler said. “In fact, he could say if they really wanted to know that, they could have asked that.”

The precision required to catch someone in a lie was a point made by Rodgers as well.

“You have to have unambiguous proof that the statement was false and that the speaker knew it to be false,” she said. “What that means as a prosecutor is that you have to be exceedingly careful and have to get kind of the perfect question and the perfect answer together.”

“As a prosecutor sometimes you’ll walk out of a courtroom and you’ll say, ‘Man, that guy lied through his teeth to me, I’ve got him!'” she said. “And then when you review the transcript, you realize that in fact there’s some ambiguity there, and you can’t say with 100 percent certainty that the statement was false, and the speaker had to know it was false, and it was intentionally false, and it was a material matter and all of those things.”

“Seasoned prosecutors walk away without having captured it in the questioning. The chance that Senator Franken — who I don’t think is even a lawyer — is going to capture that is pretty slim,” she added. “It’s very, very hard to do, and it’s hard to prove.”

There are obvious holes that Sessions could already walk through (and, in statements, has).

Even had Sessions been asked more directly — “Did you make contact with Russian officials as part of your duties with the campaign?” — Butler said he thinks Sessions could “make a credible case that the answer is no,” and that the contacts with the Russian ambassador mirrored his contacts with several dozen other ambassadors he contacted in 2016, as a senator and member of the Senate Armed Services Committee.

Sessions enjoys another protection in this case: As someone in a high-profile position, prosecution for perjury would need to be fairly open-and-shut. If you come at the king, you better not miss, as Butler put it.

“Is it a slam dunk? No,” he said. “And I don’t think you bring a case against the nation’s top law enforcement officer unless it’s a slam dunk.”