Even if you're right about Congress, there are other factors inolved. I'll repeat the following.

The Trumpster is cornered and knows it. If he fires Mueller his options for pardoning his 3 kids are gone. What Mueller would then do is turn his evidence over to the NY Attorney General who will prosecute the Trumpster and his 3 kids without the fear of any pardons. So the Trumpster has to hope Mueller will go for a pardon of his 3 kids and refer everything to a Repug Congress for impeachment regarding any criminal activity on his part. So far the Repugs have been too cowardly to stand up to the Trumpster, so this might be a good way for him to go. Also, keep in mind that the attorneys Mueller brought on board are civilian attorneys and could just as easily work for the NY Attorney General. Very little is mentioned on the news about the NY Attorney General, but he is very much there and very eager to go after the Trumpster and his crime family. No matter how this goes down, the Trumpster is toast for sure. It's just a matter of time, and time is one thing we don't have. Every day it will only get worse.