A simple point as we start the morning. The President can’t end birthright citizenship by executive order. This is a completely ridiculous idea, a sort of clown-show trial-run at rule by decree. No one with any credibility, let alone legal experts think an executive order can end birthright citizenship. There has been a push on the right to change this practice by passing a law through Congress, specifically revising Immigration and Nationality Act. This too is dubious at best, though it has been proposed and with a sufficiently partisan Supreme Court anything can be done. The change to legislate a change is best scene as a stunt not real lawmaking.
Birthright citizenship is based on the clear wording of the 14th Amendment. It’s literally the first clause: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside.”
As this historian explains in this thread, birthright citizenship was the default assumption in American law before the 14th amendment. (I strongly recommend reading that thread.) The only question was whether or not this framework was limited to white people. The debates surrounding the language makes clear that birthright citizenship specifically was what the amendment’s authors had in mind and that the need for the language was to apply it to people regardless of race. As a matter of policy you can make any arguments you want. As a matter of what the authors intended (i.e., an originalist argument) it’s really open and shut.
It’s clear that this is yet another shiny object President Trump is throwing up to grab hold of the news cycle in the final days before the midterm election. But the constitutional principle is important enough that a sturdy defense is still necessary.