In 2016 the GOP started with 16. Trump supported controlling illegal immigrants and all of the others needed the big GOP donors that supporting illegal immigration. That gave Trump a base of 25-30% and he built from there.
In 2024 illegal immigration and the Ukraine/Russia war are both issues with the establishment big GOP donors on one side, and a significant portion of the base on the other. DeSantis already waffled on Ukraine. Waffling on these two issues will be a killer for anyone running in a fair primary.
Unfortunately, Ukraine is going to be the big issue this time around.