Immigration is not my area, but every present or former DC lawyer has spent at least an hour on this.
#1: US statute is very clear. He is a natural born citizen. Natural born does not mean native born. Natural born means a citizen at the moment of birth, by operation of law. Law is very clear. Because of mother, and his later US residency, he is clearly a NB citizen.
(See US Code 1401 and Harvard Law Review http://harvardlawreview.org/2015/03/on-the-meaning-of-natural-born-citizen/)
#2: Even if there was a possibility of a successful legal challenge, the courts are very reluctant to go against voters’ choices. For example, JFK’s in actuality not winning Illinois, and therefore NOT winning the presidency, Nixon knew even though the FBI had all the evidence of election stealing vote fraud by the Chicago Daley Machine, the people thought JFK had won and the courts would have been VERY reluctant to get involved.... and Nixon declined to take the matter into the courts.
For example, SCOTUS knew they had to, but hated having to be involved in Bush v. Gore. Regardless of their ruling, they knew the case would bring nothing but bad vibes for the Court.
That’s also why many Florida District Courts kicked their 2000 election cases to Leon County. “I’m not touching that one.....”
Also, there is the standing issue. Who exactly would one sue, and what is their standing to do so. Courts do not like cases such as this.
The controlling law is the Immigration and Nationality Act, Pub. L. No. 82-414 § 301(a)(7), 66 Stat. 163, 236 (1952).
The foreign-born child is not a citizen if the citizen parent does not meet the requirements of this statute. The foreign-born child is not a
citizen by birth, the foreign-born child is a citizen by statute. http://uscode.house.gov/statviewer.htm?volume=66&page=163
Statutes “conferring citizenship upon foreign-born children of citizens” is naturalization. U.S. v. Wong Kim Ark, 169 U.S. 649, 702-703 (1898)