I've never heard of a challenge to someone's citizenship being restricted to their own party (or ANY party for that matter).Do you have a link for that?And the Democrats will do that if either one gets the nomination.Rubio is eligible, and Trumps ignorant statements just make him look like a fool. Also if you take a look a previous cases filed against the dear leader, the only entities that would have standing to challenge eligibility of a candidate are the political parties themselves.
I guess I didn't make myself clear, the republican party would have to challenge their candidate and likewise the dems would have to challenge theirs. According to previous rulings on standing it is up to the party to ensure eligibility before they place a candidate on the ballot. The one thing the courts didn't address is who ensures an independent is eligible.
I couldn't find the quote I was looking for in this link, but it gives a pretty good background and I think is a good predictor where any cases filed against Cruz or Rubio would go. Some of the cases were based on the same issues.
Barack Obama presidential eligibility litigation - Wikipedia, the free encyclopedia
What ever, the brief descriptions given in the link, like I said didn't include what I was looking for and at this point in time I not going to review them cases by case to read the actual rulings, so let's just say I misremembered and leave it at that. If you bothered to look at the cases in the link I think you will understand why a challenge will go nowhere.