What happens if it is found the president broke the law?
Charging the president with a crime is not like charging the average citizen with a crime, or even other top White House officials.
"Whether or not one can indict criminally a sitting president is an unanswered question," Susan Bloch, a constitutional law professor at Georgetown, told NBC News. "It's never happened and people are not sure whether it can."
While it's never been tested in court, many legal scholars, including Bloch, argue that the president is constitutionally protected from criminal prosecution as long as they occupy the White House. The prevailing opinion was expressed in a 1973 memo by President Richard Nixon's Solicitor General, Robert Bork, who argued that then-Vice President Spiro Agnew could face charges stemming from his time as governor of Maryland, but that a president could only be charged after leaving office.
Instead, the job of prosecuting a president would likely be left to Congress. If investigations into Trump's conduct turned up strong evidence of wrongdoing, the House could vote to impeach. The Senate would then try the president and, if two-thirds of members agreed, remove him from office.
But Congress is not a normal jury and the process could turn on political considerations as well as legal ones.
For one, the president's party currently controls both the House and Senate, which sets the bar high for any move toward impeachment. But even if Democrats were to take over, there could be factors that cause them to hesitate as well.
Rep. Adam Schiff (D-CA), the ranking Democrat on the House Intelligence Committee, suggested on Wednesday that Congress would consider the national mood toward Trump along with any hypothetical charges.
"Would the country, would the Congress, both Democrats and Republicans, view the president's conduct so serious as to be disqualifying? Or would it be viewed as just a way to nullify the election by other means?" Schiff said on MSNBC's "Morning Joe." "That's the ultimate test."
Has anything like this happened before?
The last two presidents threatened with impeachment, Bill Clinton and Richard Nixon, both faced charges of obstruction of justice along with other accusations.
In Clinton's case, he was found not guilty. Nixon resigned before the process could play out, but the House Judiciary Committee had already advanced articles of impeachment with bipartisan support. President Gerald Ford, who took over, subsequently pardoned Nixon.
It's notable that in Nixon's case, the "smoking gun" recording that preceded his resignation included audio in which the president appeared to order an aide to convince the FBI to drop its investigation of the Watergate break-in.
Michael Gerhardt, a law professor at the University of North Carolina who has written a book on the impeachment process, said there could be parallels between Nixon and Trump, but it was too early to know for sure. The charges against Nixon were far more extensive and included accusations of abuse of power.
"It doesn't mean what Trump did is not a problem, but the facts are different," Gerhardt said.
How does the latest news fit into this?
Let's go over the most recent reports: According to a source close to Comey, the former FBI director wrote a memo documenting his meeting with Trump on February 14. The existence of the memo was first reported by The New York Times and confirmed NBC News.
The meeting came the day after Trump had fired Flynn for discussing sanctions with Russian Ambassador Sergey Kislyak and misleading Vice President Mike Pence about the conversation. According to the memo, Trump spoke to Comey alone at the end of their meeting and said, "I hope you can see your way clear to letting this go, to letting Flynn go." The White House has denied anything improper.
Alex Whiting, a Harvard law professor and former federal prosecutor, told NBC News that the account of the Comey meeting was a "game changer" because it could show that Trump not only acted inappropriately but also tried to block an ongoing probe. "It's quite hard to find a proper purpose for that conversation," Whiting said.
This is important, because proving criminal intent is a prerequisite for advancing obstruction charges and it can be a difficult hurdle.
Also potentially critical is that the memo's alleged version of events connect to earlier reports and actions suggesting that the president was disturbed by Comey's investigations into Trump's associates and was willing to confront him over the issue.
The White House offered shifting explanations for Comey's removal, but Trump told NBC News' Lester Holt that his disdain for the FBI's ongoing investigation into his campaign's possible ties to Russia, which Comey confirmed in March, helped inform his thinking. Trump also called investigations into his campaign's ties to Russia "a taxpayer funded charade" on Twitter the day before firing Comey. At the same time, Trump has said he wants the investigations to continue.
Shortly after Comey's removal, sources close to Comey told news outlets, including NBC News, that Trump asked the FBI director to pledge his loyalty at a meeting in January. The next day, Trump tweeted what appeared to be a threat in which he warned that Comey "better hope that there are no 'tapes' of our conversations before he starts leaking to the press!" The White House has declined to confirm or deny whether Trump recorded their meetings, but has denied he asked Comey for his personal loyalty.
"When you put that all together with his statements and explanations and conduct, then common sense tells you that what he's trying to do is shut down this investigation," Whiting said.
Whiting was quick to add, however, that this interpretation rests on the reported allegations surrounding Trump proving to be accurate. We're still a long way from a full accounting of the relevant interactions between Trump, Comey and the FBI.