Trump, DeSantis, or any of the other GOP candidates would make a better POTUS than Biden, Harris, or any other Democrat candidate that's on the radar right now. But speaking hypothetically, if Trump continues to hold a commanding lead throughout the campaign and wins the election he will generate non-stop negative media assaults and political prosecutions for the entire six years. The Democrats will manufacture one slander after another, generate riots in the streets (like we've seen before), and the deep state within DC will resist him at every turn - just like last time. The GOP is supposed to have the advantage in winning the Senate in '24 due to the fewer seats they have to defend, but that's not a sure bet. Without the Senate, every Trump bill would be dead on arrival. One of Trump's enduring weaknesses has been the inability to surround himself with loyal, competent people, and we would probably see more cabinet turmoil and a continuous flow of leaks from anonymous sources meant to embarrass him and damage his effectiveness. Of course Trump loyalists don't foresee this scenario, but considering recent history it's almost guaranteed. If Trump fatigue sets in with the public after the first year of all this, the result would be the loss of both houses of Congress and a lame duck presidency for at least two years if not all four. Also, let's not ignore the fact that his unfavorable rating in RCP polls has held steady around 55% for the past year. Victory over Biden is not a slam dunk.
That's why the Democrats want to run against Trump - not DeSantis. That's also why Republican voters should consider what a Trump presidency would look like if he wins, and what another four years of Biden would be like if he beats Trump.