Well, you don't see this sorta thing everyday in American politics. In fact, the last (and only) time we saw a President fire someone leading an investigation into him was when Nixon fired Archibald Cox, the special prosecutor looking into the beginnings of what turned out to be the Watergate scandal which would rock the nation and make "Nixonian" synonymous with bad things.
So you can't say this is move is unprecedented, but you can say that is all very Nixonian.
FBI Director Comey was dismissed by Donald Trump on Monday via a letter from the President. In the dispatch, Trump made it a point to note that Comey had told him "on three separate occasions" that he was not under investigation for his ties to Russia, but that he felt it was right to fire Comey anyway on the recommendation of the Department of Justice. This is raising all the eyebrows because former Director Comey has made clear in public comments that the FBI was actively investigating Russia's involvement in the 2016 election, and also the extent to which Trump associates were implicated. While Comey has made no public statements about his investigation into Trump specifically, the timing of this firing, which comes as the Russia investigation has begun heating up, does not look good for Trump.
And the rationale for Trump's firing Comey is as eyebrow raising as the timing. The recommendation letter from Attorney General Jeff Sessions and deputy AG Rod J. Rosenstein has Rosentsein saying he "cannot defend the director’s handling of the conclusion of the investigation of Secretary Clinton’s emails, and I do not understand his refusal to accept the nearly universal judgment that he was mistaken.”
In other words, the stated rationale for Trump firing Comey is that Comey was not nice to Hillary Clinton during the election.
Brief note: Trump used to love how Comey was treating Hillary during the election.
Leading Dems like Chuck Schumer are hollering for a special prosecutor; leading Republican and Senate Majority Leader Mitch McConnell has rejected this. "Today we'll no doubt hear calls for a new investigation, which could only serve to impede the current work being done," McConnell said on the Senate floor. McConnell also took issue with Democrats being outraged by this firing after months of criticizing Comey for his handling of the Hillary-email investigation.