Several lawsuits and ballot challenges asserting that Cruz is ineligible to become U.S. president have been filed. No lawsuit or challenge has been successful, and in February 2016, the Illinois Board of Elections ruled in Cruz's favor, stating, "The candidate is a natural born citizen by virtue of being born in Canada to his mother who was a U.S. citizen at the time of his birth."
That does not speak well for the gop to admit a possibly ineligible candidate, but keep trying.