Of course Trump should fire Mueller, but he won’t. I think Trump sees the writing on the wall the Democrats are going to do very well come November and take both Houses of Congress. He is not going to give then any amo to impeach him with.
It would seem that the GOP hold on the Senate is safe.
Moreover, draining the swamp (especially firing Mule Face) would energize Trump’s base like nothing else. That could even improve chances of retaining control of the House.