Or to fire Mueller

Oh no, I'm assuming somebody fires Mueller or slightly smarter, accepts his report and then sits on it. But the House subcommittees can subpoena Mueller and everything he has is public. Firing Mueller serves little purpose now. The House takes over the investigation seamlessly. State AGs file charges that can't be pardoned by the President. Manafort starts his (long) prison sentence in state prisons even if Trump pardons him, for state crimes he has already plead guilty to.

Even if the Senate refuses to act, it just makes it worse for them in 2020. Democrats would take the Senate AND the Presidency.