He served one term in MA after giving the Dems everything they wanted and ruining what was left of the GOP.
You think he'll do better as a Republican POTUS? I think such a view is fatally naive.
Here is your candidate:
Enjoy defending him.
Otherwise, as happened to Ford in 1976 and Bush in 1996, conservatives back a primary challenger and, even though you win renomination, you are weakened and end up defeated for reelection.
A President Romney would be subject to the same political calculus.