Why did Trump fire Comey?

On May 3, 2017, Comey testified in a congressional hearing, but declined to answer questions about whether the President was personally under investigation. Within days, the President decided to terminate Comey. The President insisted that the termination letter, which was written for public  release , state that Comey had informed the President that he was not under investigation. The day of the firing, the White House maintained that Comey's termination resulted from independent recommendations from the Attorney General and Deputy Attorney General that Comey should be discharged for mishandling the Hillary Clinton email investigation. But the President had decided to fire Comey before hearing from the Department of Justice. The day after firing Comey , the President told Russian officials that he had "faced great pressure because of Russia, " which had been "taken off' by Comey's firing. The next day , the President acknowledged in a television interview that he was going to fire Comey regardless of the Department of Justice's recommendation and that when he "decided to just do it," he was thinking that "this thing with Trump and Russia is a made-up story." In response to a question about whether he was angry with Comey about the Russia investigation, the President said, "As far as I'm concerned , I want that thing to be absolutely done properly ," adding that firing Comey "might even lengthen out the investigation."

It is obviously the Trump fired Comey because he didn't like his testimony on May 3, 2017, where Comey refused to say that the President wasn't under investigation.

Was this obstruction of justice?  Maybe.  I think this is the worst thing that Trump did in the entire Mueller Report.  This is the smoking gun.  It is obvious that Trump didn't like the investigation and fired Comey in an attempt to "impede" the investigation.  This was the catalyst, but not the only cause, of the Mueller investigation, which started on May 17, 2017, 14 days later.

The reason I say "impede" instead of "obstruct" is because "obstruct" is a technical word.  What does it mean? Look at the statue and case law.  This will be a different post.  I will just say that "obstruction of justice" in the normal use of the term means something like destruction of documents and witness tampering.  Refusing to cooperate with an investigation is not, because you have a Fifth Amendment right not to.  What about attacking the credibility of the accuser or firing them when you have every right to?

I'm a little tired of this topic although there is more than can be said.  I will say that I think the other accusations are basically groundless.  It is not a crime to complain about being investigated.  Or to make a very bad joke about it ("hey Lewandowski, get rid of this guy, will ya"), and again make the bad joke ("Priebus, I want you to stop this thing"), to try to flatter the investigator ("hey Christie, call Comey and tell him I like him") or to complain that your attorney (Sessions) isn't doing his job, or to muse out loud that one of your associates "should stay stay strong and not flip and maybe there will be a pardon in it for you" or even to send a weird message to a witness against you ("Cohen baby, remember the bossman loves you").

I think that Trump firing Comey is the only valid accusation of the batch.  Is it obstruction?  I will attempt to answer that honestly later.