From a Little Birdie on Trump winning the birthright citizenship battle at the Supreme Court (where this will ultimately go): "The best argument is that a president has power to end birthright citizenship if its an invasion. Whoever on Trump's team that crafted his EO appears to be following an opinion from Federal Judge Jim Ho making that case (or what we call in my legal circles "The Ho Invasion Theory"). I'm not sure even Clarence Thomas agrees yet with ending birthright citizenship whole cloth. But I do think more judges would be willing to sign on to ending it...