The President needs to act now. He is at a point of maximum political power. He should fire Rosenstein and make Pruitt acting Deputy AG. Or fire Sessions and make Pruitt acting AG. So what if the usual suspects whine. So what if they pass legislation purporting to protect Mueller. Trump can campaign in the fall against any Rep or Senator (those up for election) who vote to override his veto. Please just do it!
There's no evidence for that. Trump has been steadily gaining as the economy improves and the economy has a lot more improvement ahead of it. Trump is gaining on foreign policy. Trump is generally making good on his MAGA promises. He is not peaking, but if he takes the advice of the obsessive types, he will risk having a push for impeachment.