And that probably bugged Dolt 45 at least a little. The real reasons, of course, have been amply described. Comey is a guy who, perhaps arrogantly, follows his own rules. His mishandling of the Clinton emails was, perhaps, not so much a partisan move as an attempt to show off what a Dudley Do-Right sort of guy he is - instead of simply stating that the FBI found no evidence of any criminal act and leaving it at that, as he should have done, he launched into his own opinion that Clinton acted improperly, though not illegally, because that bothered him personally. He's entitled to his opinion, of course; but as FBI director he had no business appending it to his factual determination. Then in October there's his infamous letter, which was much more damaging because of the timing. The other day Comey testified that he sent the letter because he felt the need to protect the reputation of the FBI - apparently concluding that protecting the reputation of the FBI (and by inference, himself) was more important than risking influencing an election. If that was his true motive it's as bad, for its arrogance, as if his motive had been partisan.
All this said, on occasion Comey's self-styled Dudley Do-Right persona has also led to positive results, as when in 2004 he prevented Bush officials Gonzales and Card from taking advantage of John Ashcroft's serious illness to get him to sign an extension of a warrantless wiretap order. More about this incident here: https://thinkprogress.org/comey-breaks-silence-white-house-tried-to-force-incapacitated-ashcroft-to-back-spying-program-66fb293ac29 This incident was one of the reasons Obama hired him. The point is, though, that for good or ill Comey seems to be someone who does his own thing and tends not to knuckle under to much of anybody. For an authoritarian like Trump this quality could not be tolerated. It was apparent to Trump that Comey was going to proceed with the Russia investigation as diligently as he could, regardless of what he might have been told or leaned on to do. Plus, he's 6'8". So he had to go.
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