SCOTUS opinion that being born in the US means you are a "natural born citizen" and that said nothing about the citizenship of either parent. (Remember the standards for citizenship in general are not necessarily the same as the Constitutional standard of "natural born citizen." Congress can decide the former; the SCOTUS is the only authoritative word on the latter as to the POTUS.)
Even though that SCOTUS verbiage was only a dictum, people inferred that being born outside the US might mean that one is not a "natural born citizen" for purposes of qualifying for the Presidency. On the flip side, also inferred from that dictum that, if someone WAS born in the US, parents' citizenship is irrelevant. The latter does make sense since, just before the constitution was adopted, no one was a US citizen and the parents of a lot of the population were immigrants. For example, Paul Revere's dad was a French citizen, yet I feel sure Revere would have been allowed to run for President.
AFAIK, the election of 2008 was the first time this became such an issue at the level it did, even though we apparently have had at least one President born in Canada. I cannot swear to this, but, IIRC, neither of his parents were US citizens, at least not at the time of his birth. Mostly, we seem to have pretty much ignored the issue, until people inside the Clinton primary campaign of 2008 birthed the birther issue as to Obama.
While I do not approve in the least of what was done during the 2008 primary or how it was done, I also do not approve of ignoring any provision of the Constitution. I think someone should check something before a candidate for POTUS is allowed to get on primary ballots.
It's too bad our Supreme Court decided it should not give advisory opinions. It would be nice to have a clear standard before someone is ensconced in the Oval Office and we have to start wondering if all his or her Executive Orders and all the bills he or she signed are actually valid under the Constitution.
I do agree that Cruz is probably OK, but not because we have any SCOTUS precedent interpreting the wording in Article II of the Constitution that requires the President to be a "natural born citizen."