If Biden is their nominee, Trump beats him big. They know this, they have only a few months to their convention to get him out and get his replacement in.
Not really. Trump did a couple of fantastic paradigm shifting things (China, energy, reshoring), but he also landed the GOP in the poo with abortion, abortion, more abortion, and did I mention abortion?
Trump could beat Michelle any day and any way, but probably not Biden, not once the primary is over, the party is stuck with their nominee, and the knives come out.
They have about 14 months.