OTOH he could run for VP. Then were the new president to resigned or die then Trump could serve a third (un-elected) term as president! Rinse, repeat!8-))
No, he can't. The elected VP also has to be eligible to be elected as president.
The 12th Amendment says:
> But no person constitutionally ineligible to the office of President shall be eligible to that of Vice-President of the United States.
Paired with the 22nd which restricts Presidential eligibility, Trump cannot be elected as VP. He could potentially (this would go through the courts, it is a gray area) be nominated to VP, but he cannot be elected as President or VP again.
Melania is not a natural born US citizen so that would be impossible
What if he runs in 2028 and the Supreme Court declines to rule on anything other than preventing the states from banning him from the ballot like they did in Colorado?
Edit: or in light of Trump v. Anderson