Manchin, and he would appoint Richard Ojeda to fill his seat
Doubtful. He'd appoint some DINO because he thinks only such an win the next election. However, if Manchin runs and wins, I'd expect the Republican legislature to change to laws and require a special election within 90 days. Manchin could do nothing about it because he has no veto power or they pass such a bill during the lame duck session.
If there is a single forward thinking bone in Joe Manchin's body -- which there may well not be -- he would appoint Carte Goodwin
again. Carte's brother, Booth, who is a former US Attorney, or his sister-in-law, Amy, who is the Mayor of Charleston, could also make good appointees.
