A source close to Comey confirmed to ABC News that the former FBI director, who was fired last week, was asked by Trump in February to end the FBI probe into ties between Flynn and Russia, according to a memo Comey wrote about his conversation with the president.
In the memo, which was shared with top FBI associates, Comey wrote that Trump said "I hope you can let this go," in relation to the investigation into Flynn's actions, according to a source who read the memo.
"I hope you can see your way clear to letting this go, to letting Flynn go," Trump said to Comey, according to the source. "He is a good guy. I hope you can let this go."
ABC News has not seen the memo and Comey has not commented on the matter.
The White House has denied that Trump tried to block the probe, saying in a statement, "While the president has repeatedly expressed his view that General Flynn is a decent man who served and protected our country, the president has never asked Mr. Comey or anyone else to end any investigation, including any investigation involving General Flynn."
"The president has the utmost respect for our law enforcement agencies, and all investigations," the statement continues. "This is not a truthful or accurate portrayal of the conversation between the president and Mr. Comey."
The New York Times was the first on Tuesday to report the discussion and subsequent memo.
Sen. Chris Murphy, D-Conn., posted The New York Times article on Twitter along with the comments, "Just leaving Senate floor. Lots of chatter from [Democrats] and [Republicans] about the exact definition of 'obstruction of justice.'"
House Minority Leader Nancy Pelosi, D-Calif., said in a statement Tuesday, "If these reports are true, the president's brazen attempt to shut down the FBI's investigation of Michael Flynn is an assault on the rule of law that is fundamental to our democracy. At best, President Trump has committed a grave abuse of executive power. At worst, he has obstructed justice."
So what is obstruction of justice and could it apply to the president?
What is obstruction of justice?Obstruction of justice is a federal crime in which someone "corruptly" attempts to "influence, obstruct or impede" the "due and proper administration of the law" in a pending proceeding, as stated in 18 U.S.Code 1505.
"Corruptly" is defined in an accompanying section, 18 U.S.Code 1515 (b), as "acting with an improper purpose, personally or by influencing another, including making a false or misleading statement, or withholding, concealing, altering, or destroying a document or other information."
Liza Goitein, a former trial attorney for the U.S. Department of Justice who currently co-directs the Liberty and National Security Program at the Brennan Center for Justice at New York University Law School, put the statute in simpler terms.
"To boil this down, if the president corruptly attempted to influence the due administration of justice, that is obstruction of justice under the statute," Goitein told ABC News. "This is an incredibly serious offense."
If the description of Comey's memo is accurate, does it detail actions that meet the definition of obstruction of justice?Some legal experts say "yes."
"This looks very much like obstruction of justice," Goitein told ABC News. "It's hard to reach a different conclusion. It is certainly possible that he incorrectly remembered the conversation or misrepresented it. But there's no reason to think that's the case."
David Shapiro, a former FBI special agent and now an assistant professor at John Jay College of Criminal Justice, told ABC News, "It's hard to view this as anything other than obstruction of justice."
Laurence Tribe, professor of constitutional law at Harvard Law School, told ABC News that if Comey's memo is accurately reported, then he believes it describes "an impeachable attempt to obstruct justice."
John Lauro, a defense attorney with the Lauro Law Firm based in Tampa and New York City, told ABC News it remains unclear whether Trump obstructed justice.
"It depends on the evidence, which right now amounts to triple and quadruple hearsay," Lauro said. "If Comey felt there was obstruction he would have been obligated to advise the Attorney General and formally open an investigation, none of which appears to have happened."
David McIntosh, a lawyer and former congressman who is now the co-founder of the Federalist Society for Law and Public Policy Studies in Washington, D.C., defended Trump, saying the president "acted appropriately" if he was providing guidance to Comey on the investigation.
"It is important for us to step back and remember that, under the Constitution, the president has the authority and power to enforce the laws," McIntosh said at a press conference Wednesday morning. "The FBI director reports to the president and it is the president's decision to delegate authority on investigations. In delegating that authority, presidents have wisely chosen to insulate the FBI from political interference. But the president still has the power and authority to direct the FBI how to do their job."
What are the potential legal ramifications?Congress can launch an investigation into whether Trump's actions amount to obstruction of justice, and the legislative body can issue a subpoena to obtain Comey's memo as evidence if necessary, according to ranking member of the House Intelligence Committee Rep. Adam Schiff.
Schiff said that Congress may be preparing to do so.
"Congress will need to subpoena them if indeed they're not provided voluntarily. I certainly support that. I think there are many committees that will," Schiff, D-Calif., told ABC News chief anchor George Stephanopoulos in an interview today on "Good Morning America."
Legal experts said Congress can also subpoena other documented communications between Comey and Trump, including any recorded conversations or meetings.
"The key evidence is the notes that Comey took," Shapiro told ABC News. "Corrupt intent is required to prove obstruction of justice. Comey's firing fits into the greater picture there."
Legal experts said obstruction of justice, if proven to be true, is a high crime and could be an impeachable offense.
Impeachment is a political process in which any civil officer, including a president and vice president, can be removed from office "for, and conviction of, treason, bribery, or other high crimes and misdemeanors," according to the Article II, Section 4 of the U.S. Constitution.
New York-based criminal defense lawyer Ronald Kuby told ABC News there is no definition of "high crimes and misdemeanors," but rather "it's whatever Congress thinks it should."
The House of Representatives wields the sole power to impeach a federal official, and the Senate has the sole power to convict and remove the individual.
The House needs a simple majority vote to approve an article of impeachment, which can be brought by any member. If the House votes to impeach an official, the case must then be presented to the Senate, which will hold a trial. The Senate needs a two-thirds majority to find the official guilty and remove him or her from office.
Ultimately, some legal experts said, it's unrealistic to expect the Justice Department to file criminal charges against Trump -- and it might not be legally possible. Impeachment would be the only process through which a charge of obstruction of justice could realistically be brought against Trump, experts noted.
"No sitting president has ever been prosecuted for any crime," Goitein told ABC News. "So that seems unlikely."
ABC News' Jack Date, Lauren Pearle, Kate Shaw, Benjamin Siegel, Pierre Thomas and Cecilia Vega contributed to this report.