[gdani]

If the question is the nomination, the challenge is not premature during the nomination process.

I would argue it's moot for the party nomination as there is zero requirement that someone be a natural born citizen to become a party's nominee. Only to become president.

If they wanted, I think a party could nominate just about anyone regardless of age, citizenship, etc. But it does not mean they would qualify to be president.

[Cboldt]

That's a reasonable argument in the general election, but the state has an interest in protecting the public from a fraudulent primary ballot.

We're a long way from the process as envisioned by the founders. First presidential primary was held in 1921. Before that, parties chose nominees in smoky backrooms.

[frog in a pot]

... there is zero requirement that someone be a natural born citizen to become a party's nominee...

IIRC, primary candidates are required by most or all states to sign a declaration they are eligible to run for the presidency in the general election.