If he had half a brain, Trump would pick a candidate from one of five states Biden took back - that might lock one down, but my guess it will be a weaselly ass kisser who won't make Trump look lame.
Scott Walker? That would be from left field but check the boxes. But he lost a race.
JD Vance isn't from one of those states, but is adjacent to the three biggies.
He's at war with the Georgia Democratic party save for MTG - I think with MTG even Biden wins by 10.
He's at war with Flake and Ducey, Kari Lake wants to be a Senator. She'd take it but be poison.
I predict Vance, who completes a Paul Ryan-esque trajectory and goes to work at FOX. IFF Biden drops out.