Manchin may well be finished in WV if he does. Trump will go after him, for sure.
Manchin, like Romney, is not up for re election until 2024. 4 years is an eternity in politics, and Trump will either be a lame duck, or 4 years out of office by then. Were either of their seats up in 2020, both would have already declared their votes for no witnesses and acquittal.