Minor v. Happersett says that natural born citizens are “children born in a country, of parents who were its citizens”. It does not explicitly state that the parents had to have been its citizens at the time of the birth of the child, and therefore an argument can be made that a person born in the US to people who subsequently because US citizens became a natural born citizen when his parents became US citizens. I have not seen this analysis before, and perhaps it is flawed, but I believe it is not inconsistent with the language of the holding in Minor.
Rubio’s father did become a US citizen following Marco’s birth; to my knowledge Barack Hussein Obama I never did become a US citizen.
Interesting to know (and no, Obama’s father didn’t become a citizen, he moved back to Kenya shortly after O’s birth and per Dreams of My Father, he only visited O in the US once and it was just a quick meeting).