A little late on the response here but the question was worthy of a response.

It's hard to say what's really going on in my opinion. I see tons of allegations but very little proof. Lots of suspicious behavior but no smoking gun. I think there is some evidence of Trump dealings with Russian oligarchs but not regarding Russian election interference. We have learned of a meeting with Trump Jr. but again, more smoke but no fire.

I think Trump firing him was his way of showing what he does to those whom he doesn't trust and/or don't convey full loyalty towards. Is he dumb enough not to realize the rest of the FBI is still there to continue the investigation?