if ihey want to pursue a republican agenda, trump is mostly letting them, why rock the boat?
You have to look at what Trump has delivered for GOP and what he is likely to be capable of delivering after the midterms.
So far, tax cuts, and soon, the second conservative Supreme Court justice.
Congress is almost certain to go Democrat in the midterms, after which time they can expect nothing else of substance.
It may be convention to allow the incumbent POTUS a clean run at the next presidential election, but I’m sure there are some calculations going on as to whether he’s going to even make it to 2020 due to Mueller, in which case he probably needs to get the push sooner to give someone else a realistic chance.