You'll have to show that one. The Constitution only states that you have to be a "natural born citizen". That does not mean it has to be on US soil.
The laws that govern whom is a citizen at birth have changed many times, so there are a lot of variables that can come into play. However, you don't have to have been born on US soil, regardless of when you were born. McCain would qualify even if he had been born in Vietnam.
U.S. Code 1401, which was cited earlier, is the current law (since I believe 1986), but doesn't apply to people born earlier. Per interpretations cited by the U.S. Citizenship and Immigration Services (Department of Homeland Security), the law that was in effect at the time governs. A lot of the new code is consistent with the laws of the past though.
That having been said, someone born abroad to two U.S. citizens, in wedlock, has always legally been a citizen at birth, so long as one of their parents resided in the U.S. at some time prior to their birth. During some time periods the law required that person to take up residence within the U.S. for some period in order to retain that citizenship status, perhaps that is what wintersprings is referring to. (How long someone had to reside in the U.S. to retain citizenship, and during which age ranges that residence had to occur, depends on exactly when they were born and whether or not both parents were citizens.)
One thing that is changed in the new code is in regard to someone born abroad to one citizen parent and one alien, in wedlock. Under previous laws, the citizen parent had to have resided in the U.S. for 10 years, at least 5 after they turned 14, in order to confer citizenship at birth to their child. Also or note, at different times there were various laws that counted the parent's military service as residence in the U.S. for purposes of fulfilling those residency requirements.
Here is a fairly comprehensive list of interpretations cited by the USCIS which govern citizenship status for people born at different times and under different circumstances.