Trump's best bet - a strong one, I think, as a non-lawyer - is Section 5 of the Amendment, which seems not to get much attention in these discussions:

"The Congress shall have the power to enforce, by appropriate legislation, the provisions of this article."

He can argue that it takes an act of Congress to disqualify a candidate in a national election and possibly in a state primary as well.

Admittedly it doesn't say "Congress alone," but interpretation will be up to the Supreme court.