My guess is that Romney is planning to be the Republican nominee for 2020. He expects Trump to fold under the treat of impeachment or be impeached and convicted, and he is going to do everything he can to move that along. Like all Never Trumpers, Romney flourishes on delusion that once Trump is out of the picture, which they see as inevitable, the Republican masses will turn to him and the other GOPe stalwarts as their saviors.
He doesn’t know Trump very well, does he?
I think you’re right. If he can help the Democrats force Trump out then he believes the Republican establishment will turn to him as the 2020 nominee. The Democratic candidates are so awful he probably figures he would stroll right into the White House.