The White House disputed the account of the Comey memo.
What is obstruction of justice?
An obstruction of justice charge could be brought against anyone who attempts to influence or obstruct official investigations. It is a federal offense. The statutes – and there are several – that cover obstruction of justice allow for prosecution of a person who “obstructs, influences or impedes any official proceeding.”
If Comey’s memo is proven to be accurate, is what the president did obstruction of justice?
It could be. But proving that someone was trying to interfere with an investigation by suggesting it be ended is tough to prove. According to an Associated Press story, 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."
How would the attempt to influence the investigation be proven?
Comey's memo could be evidence of obstruction, along with Comey's testimony if there were a trial.
If there is a recording of the meeting, as the president hinted at in a tweet last week, that could help prosecutors decide the president's intent if he made comments to Comey about ending the Flynn investigation.
"What you have is contemporaneous documentation of Comey's recollection of what the president said," Bob Bauer, who served as White House counsel under President Barack Obama, told the AP. "That's obviously a very powerful piece of evidence."
Former prosecutor Jonathan Lopez pointed out that without recordings, the memo is a case of "he said, she said.”
Does it matter that a request to end an investigation comes from the president?
Julie O'Sullivan, a former federal prosecutor who now teaches law at Georgetown University, told The New York Times that President Trump is "building a beautiful case against himself." She said because of the relationship between a president and an FBI director, a request to end an investigation could rise to the level of obstruction.
If a charge of obstruction were proven to be true, can the president be indicted?
Legal opinions on two separate occasions from the Justice Department concluded that criminally prosecuting a sitting president would undermine his or her ability to perform the duties of the executive branch.
So the short answer is no.
One of the opinions – written in 2000 when charges of obstruction of justice were being leveled at former president Bill Clinton – read: "Our view remains that a sitting President is constitutionally immune from indictment and criminal prosecution."
The other opinion was from 1973 and was written when charges of obstruction of justice were made against President Richard Nixon.
What about impeachment?
Can a president be impeached for obstruction of justice? Yes. Both presidents who have faced impeachment – Richard Nixon and Bill Clinton – were accused of obstruction of justice.
But remember, impeachment is a political process, and right now, both the House of Representatives – the body that would bring impeachment charges – and the Senate – the body that would conduct the “trial” for impeachment – have Republican majorities.
The Constitution says that a president can be removed from office if he has committed “treason, bribery, or other high crimes and misdemeanors.”
The standard of what constitutes "high crimes and misdemeanors is vague, and can be defined by the Congress in an impeachment proceeding.
The Associated Press contributed to this story