Republicans are going along with Trump because Justice Kennedy is going to retire soon
And they want to make sure another far right wing conservative is put on the Supreme Court.
This is why nothing that Trump says or does matters much to his Republican supporters (both the voters, but, particularly, the Congresspeople).
They believe (correctly) that putting a RW judge on the court will impact the country for decades to come and are willing to roll with whatever nonsense Trump throws at them to ensure that this is the case.
A Republican or two may make a little bit of noise about all of the Trump shenanigans, but, in the end, they will justify, excuse, or ignore the awful things he continues to do - because of the court pick.
Also, they think they can get their other right wing agenda items passed as long as they have Trump in place as their figurehead. Let him say and do crazy things, but quietly get legislation passed to suit their ends.
I believe that Republicans will never make any serious moves against Trump for these reasons, primary among them being:
Moving the Supreme Court to the Right.