If DeSantis nevertheless runs against Trump, even when Trump attacks him, DeSantis ought to be nothing but complimentary and respectful of Trump and full of praise for his accomplishments as President. In effect, DeSantis would then be running as Trump's successor, not as his opponent, and would direct his attacks on Biden and the Democrats.
Trump and the Democrats would be utterly flummoxed if DeSantis took that approach. And DeSantis might manage to pry the GOP base away from their support for Trump without wrecking the party.
Flummoxed is a great word.