The devil is in the details, of translating a noun, “supremacy” of the Supremacy Clause, to a verb, “preempt”, with the adverbs “broadly” or “narrowly.”
Trump’s appeal will be broadly based on the Supremacy Clause. By use of the Supremacy Clause, the Federal Election Commission claims broad preemption of state election laws. This includes, as a debatable point of law, denial of the right of a state to enforce federal election statutes.
While the Federal Election Commission claims broad preemption, the actual case law favors the prosecution.
The case law favors the prosecution; appeals courts have allowed incidental use of federal election statutes, where the federal statutes are not actually subject to prosecution in a state court.