@gkmizuno but the court did not say that the Constitution can only be enforced by a law signed by Congress.

What it said was much narrower, much more specific.

What it said was that state actors can't use this particular constitutional provision as basis for action against a candidate without federal authority.

The Constitution can be enforced in many ways with and without congressional legislation, it's just that states can't use this federal claim in their election systems.

It's not a paradox, it's a detail of what the court said is the constitutional design.