The exact terms of birthright citizenship are laid out in the 8 U.S.C. § 1401; the way that this is interpreted is up to courts.

According to US statute, if Barack Obama had been born outside of the US (he was born in Hawai'i) to his American mother while she was not married to his Kenyan father (...and they were married at the time he was born) , he still would have been a natural born citizen according to 8 U.S.C. § 1409.c, because she was both a citizen and had resided in the US for at least one year.

Rights are rarely absolute, or nearly as cut and dry as people claim. For instance, the freedom of the press has been interpreted to not include material that is obscene. Freedom of peaceable assembly requires that you pay a fee and get a permit. The right to keep and bear arms has been determined to not include things like buying surface-to-air missiles from Victor Bout. Up until Escobedo v. Illinois (1964), despite the 6th amendment saying that you have the right to "have the Assistance of Counsel for [your] defence [sic]", indigent suspects were not provided with an attorney (...and what use is and enumerated right if you lack the ability to exercise the right?). Under fairly recent court rulings, you must explicitly invoke your 5th amendment right to remain silent; simply being silent is insufficient.

Do I think that Trump is going to be able to revoke the citizenship of people that were born here to undocumented immigrants? No. Do I want him to? Also no. Do I want to see his mass deportations blow up in his face and implode the economy? Oh yeah, definitely. I want people--Trump MAGAts--to see just how much we rely on the underpaid labor of the undocumented people in this country for the necessities of life.