It may be that Comey's handling of the email investigation during the election was egregious enough to can him, but the circumstances and timing are bizarre.
Reasonable normie: It is horrid PR. Trump (or his advisers) must know how bad it looks to fire someone who is investigating you and even worse when a pattern emerges. Could they really be that naive to think they can control the narrative on this story?
Paranoid conspiracist: It is a way to fan into flame the slow burning Russia story to distract from something else (healthcare, nepotism, budget, lies ...) Are they that clever? Is it a necessary step towards appointing a stooge?
The simpler explanation is that Trump's administration is inept or misinformed but those are worrying conclusions.
Cromey told everyone that Hillary was guilty. But she had no intent to be guilty. So its all good.
He did not seem like a man doing his job.