This has been the GoP stance pretty much since Trump named Pence as his running mate, privately if not publically. However, having Republicans impeaching a Republican president would require that Trump become toxic politically to the various senators. This is so the Republicans can tout impeaching Trump as "putting country before party, doing the best for the people and following the will of the people" yada yada yada. It likely won't happen for a few months.
It can't happen soon enough for me. I may disagree with Pence's policies, but at least I believe he'd be a more sane, stable leader.