They have impeached already, multiple times.
During his last term yes, during this term no they haven't.
They could at least be pushing for this, there's a few republicans on the out of Trumps circle, maybe they could make some movement. Instead they sit around and do nothing, letting the crimes take place with no attempt to even declare it as wrong.
Every day is an endless stream of media and commentary on the illegal things he's doing with no accountability. Even in the highly unlikely event of an impeachment conviction, I don't see how that changes anything from a practical standpoint. The DoJ isn't going to enforce the conviction, and military leadership has steadily been replaced with yes-people since the admin took office.