Firing the guy directing the investigation into Trump’s campaign and it’s dealings with Russia to influence (i.e. win) an election does.
The issue of obstruction of justice is so obvious, it is amazing that the rightwingers on this board don't get it.
Definition: the crime or act of willfully interfering with the process of
justice and
law especially by influencing, threatening, harming, or impeding a witness, potential witness, juror, or judicial or
legal officer or by furnishing false information in or otherwise impeding an investigation or
legal process ...
Trump tried to impede the investigation into Flynn's Russia connection by asking Comey to backoff. When Comey didn't back off, he fired him. He was trying to influence and impede the investigation and the legal process. His telling Comey he 'hoped' he could let the investigation go and at the same time asking Comey if he wanted to keep his job was a threat. When Comey didn't back off, he fired him.
It's really very obvious to anyone who can think about it in an unbiased way. If your boss 'suggested' you stop doing something and you continued to do it, and then he/she fired you, you would believe you were fired for not doing what the boss wanted, especially if up until that time he/she had nothing but praise for you.