Who is the White House counsel who reportedly threatened to resign?

— -- The White House counsel who, according to a source, was among the staff who were against any notion of President Donald Trump's firing special counsel Robert Mueller last year stays mostly behind the scenes. But counsel Don McGahn has had a role in a few significant moments in the Trump administration.

The latest to come to light, according to a source is when McGahn and other White House attorneys and aides made clear they were not in favor of Trump's firing special counsel Mueller last June when the president wanted to do just that.

According to the source, McGahn has considered resigning on at least two occasions but the source did not know whether those considerations dealt specifically with the potential firing of Mueller.

The saga around Trump's desire to to fire the special counsel isn't the first time McGahn has been a key player in the inner workings of the White House. He has been part of Trump's team since the transition.

"Don has a brilliant legal mind, excellent character and a deep understanding of constitutional law," Trump said of McGahn in a statement announcing his selection as White House counsel in November 2016.

The Wall Street Journal reported that McGahn first met Trump in 2014 when the then-real estate mogul was exploring a presidential run.

After his appointment to the post, McGahn's name came up in relation to the dismissal of then-National Security Adviser Michael Flynn. Less than a week after Trump's inauguration in January 2017, then-acting Attorney General Sally Yates warned McGahn as White House counsel that Russia might be trying to blackmail Flynn, according to Yates' testimony to Congress in May.

Following Yates' warning to McGahn, on Jan. 26, 2017, McGahn briefed the president and a small group of aides. The president asked McGahn to determine whether there were legal concerns surrounding Yates' claims about Flynn. McGahn determined “within several days” there was not a legal issue, then-press secretary Sean Spicer said at the time.

McGahn was also reportedly involved in events surrounding Attorney General Jeff Sessions' recusing himself from the Russian investigation. Earlier this month, the Associated Press reported that Trump urged McGahn to convince the attorney general not to take that step. The AP cited three anonymous sources saying McGahn spoke to Sessions and encouraged him not to recuse himself. But Sessions announced his decision to do just that on March 2.

McGahn's position as White House counsel is not his first role in government. Back in 2008, then-President George W. Bush appointed McGahn to the Federal Election Commission on which he served until 2013.

According to his biography on the FEC website, McGahn worked at a Washington law firm and specialized in election law and was previously the general counsel for the National Republican Congressional Committee and the Illinois Republican Party.

He attended the University of Notre Dame, the U.S. Naval Academy, and Georgetown University's law school, the FEC site states.