This is not surprising.
Impeachment has backfired on Republicans in 90s, as Americans, deep inside, are very much against mere idea of politicians trying to undo the choice of voters. And unless there is a smoking gun bulletproof criminal case against a President, it is considered as just that - political attempt to undo an electoral choice. And will never prove longterm beneficial for whoever does that ..
4th year of Trump term is up and people see the results. In economy first of all.
And it does sink into people's minds that what mainstream media and Demparty were doing last three years were nothing but a major act of national sabotage. Mostly failed.