Some lawmakers are accusing President Donald Trump of obstruction of justice after revelations that FBI Director James Comey wrote a private account of the president asking him to shut down an investigation into former national security adviser Michael Flynn.

Congressional Democrats were already concerned that Trump was trying to stifle a probe into possible coordination between his campaign and Russia’s election meddling by firing Comey last week. The latest development only heightened their outrage, renewing calls for a special prosecutor. And Connecticut Sen. Richard Blumenthal said in a statement that “we are witnessing an obstruction of justice case unfolding in real time.”

But obstruction of justice is a tricky issue both criminally and politically. And legal experts say it could be difficult to prove the president crossed a line.

Some questions and answers about obstruction of justice:

WHAT IS OBSTRUCTION OF JUSTICE?

Simply put, it’s preventing authorities — such as police or prosecutors — from doing the work of investigating and applying the law.

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WHAT IS TRUMP ACCUSED OF DOING?

Comey wrote that Trump asked him to end an investigation into Flynn during a February meeting in the Oval Office. Comey, who was known to keep a paper trail of sensitive meetings, chronicled the president’s request in a memo he produced soon after the conversation, according to a Comey associate who reviewed the document and spoke to AP on condition of anonymity. Flynn had just been forced to resign after lying about the nature of his contacts with the Russian ambassador.

The White House disputed the account of the Comey memo.

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IS SUCH A REQUEST OBSTRUCTION OF JUSTICE?

Criminally speaking, obstructing justice applies to a variety of scenarios — like threatening a juror, retaliating against a witness, or impeding a grand jury proceeding — and Trump’s alleged request would not fit neatly into any of them, legal experts said.

“No one would write a federal statute with this situation in mind because it’s such an extraordinary situation,” said Jens David Ohlin, a dean at Cornell University Law School.

Meddling in a federal investigation could qualify as impeding a judicial proceeding under the obstruction statute. But to bring an obstruction charge, a prosecutor would have to show the president was trying to “corruptly” influence the investigation, and proving an improper intent can be hard.

Jonathan Turley, a law professor at George Washington University, said Trump would have some lines of defense.

“The president can claim he was raising an issue of concern for a longtime associate,” Turley said. “That doesn’t mean that the question was not wildly improper, and frankly, would border on the moronic.”

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BUT ISN’T THERE EVIDENCE?

Comey’s memos could be valuable in any obstruction investigation.

“What you have is contemporaneous documentation of Comey’s recollection of what the president said,” said Bob Bauer, who served as White House counsel under President Barack Obama. “That’s obviously a very powerful piece of evidence.”

But barring recordings, a memo still becomes a case of “he said, she said,” said former prosecutor Jonathan Lopez.

Still, there’s also a witness: Comey.

“He’s around and the best evidence of what happened in that meeting would be to call him as a witness,” said Barbara McQuade, former U.S. attorney for the Eastern District of Michigan.

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ARE THERE OTHER POSSIBLE ACTIONS?

Even if this didn’t lead to a criminal conviction, such a request could add to the basis for impeachment for obstruction of justice.

“It’s the whole pattern here, it’s firing Comey and also directing him to end the investigation against Flynn, all of these things are done because he wants to stop an investigation from reaching the highest echelons of the administration and possibly him personally,” Ohlin said. “It’s the type of political self-dealing that is intolerable.”

But Turley said that may not be enough.

“What we have is a memo of a president asking highly inappropriate questions of an FBI director,” he said. “This would be pretty thin soup for even an impeachment proceeding.”

(AP)