DeSantis only gets 18% versus Trump's 58% in this Morning Consult poll of the 2024 GOP primary.
Trump is averaging at least 51% in RealClearPolitics' running average. DeSantis only 23%.
If you narrow the field down to only Trump and DeSantis, Trump still beats DeSantis by ~10 points with a comfortable 44% in YouGov polling.
Even if we focus solely on Florida, DeSantis only narrowly beats Trump 47-45% in a head to head poll by University of North Florida.
Of course the actual primary isn't going to begin as a head to head matchup and DeSantis' support will be diluted. And the GOP primary system has a lot of winner take all or winner take most contests, so Trump polling at least 51% or even a strong plurality at 44% is more than enough to secure the necessary delegates even if he didn't win say Florida or New Hampshire.
Trump's favorability is still in the 80s. About 70% of Republicans think Trump actually won in 2020. It is still very much his party and his nomination. I'm especially curious how DeSantis will position himself against Trump without risking alienating the MAGA base. It is easy to think that Never Trumpers and others that are uneasy about another Trump run would support DeSantis, but the bigger question is if DeSantis can pull away Trump supporters and we haven't seen that yet.