Trump would be best as VP to Desantis. Trump's role would be to give weekly or nightly updates and to deal with the media. I think people forget how Trump and his administration gave broadcasts almost every single day about the status of COVID. Yet Biden can't even answer unscripted questions and they drag him out for the bare minimum to make a public appearance a few times a month. Trump's greatest skill is his ability to fuck with the media and cause liberals to get angry and show their worst. He is not a politician. He needs to be in a place where he can weaken his political opponents while someone more experienced with politics can get things done. But regarding your question, I believe the law states you have to *serve* two terms to be ineligible. Even if he won the 2020 election, he didn't serve a term so he'd be a possible candidate.