Whitmer I reckon, Progressive governor of a swing state, and who knows first hand that the ultra right are fucking dangerous loons that need the hand of God brought down on them.
Trump won't win the nomination in 2028, so if he's still alive and still semi-intelligable, he'll launch a third party campaign that splits the conservative vote and gives the Dems 4 more years. You saw it here first.
Manchin (though I doubt the democrats would allow it)
Honestly, if he announces his candidacy for 2024, I suspect a chunk of the "You're a Trump supporter if you are even slightly dissatisfied with Biden" crowd will happily jump ship.