In 1920, my maternal grandparents and their 5 children immigrated to the United States from Catania in Sicily. Many of their countrymen had made that same journey in the half-century since Italian unification. Why exactly my grandparents chose to cross the Atlantic then I do not know, and there is now no one left to amplify that part of the story. In any case, after settling in New York, they had one more child, my mother, born in 1922. Sometime thereafter, my grandparents and the younger children returned to Italy, leaving the two oldest to make their own way in America. By 1930, however, they decided to return to New York. Immigration was more difficult then than it had been a decade earlier. But they were able to return and reunite the family thanks to my mother's American citizenship. For all the vile nativism in vogue at that time, my mother's U,S, citizenship was not in doubt. If instead President Trump or someone with similar views to his had been able to alter American history, my mother might have had to remain in Italy. Whatever would have happened to her, had she survived the Second World War, she would almost certainly not have met and married my father, and I would never have ever existed! Thanks be to God - and the 14th Amendment to the U.S. Constitution - they did meet, and I do exist.
The constitutional text is clear. All persons born or naturalized in the United States and subject to the jurisdiction thereof, are citizens of the United States (amendment 14, Section 1). The Civil War had undone the Supreme Court's evil Dred Scott Decision on the battlefield, and the 14th Amendment then codified the consequences of that victory in the Constitution, settling the status of freed slaves and their descendants as citizens once and for all. Since then, generations of immigrants have benefited from this constitutional provision, and this country has grown great thanks to them and their descendants.
Now president Trump claims the constitutional guarantee of citizenship can be undone - not by a constitutional amendment but by a mere Executive Order - about as brazenly unconstitutional a claim as such claims get. Perhaps he is just trying to ensure that his supporters get out and vote, making his pre-election "closing argument." Perhaps, he actually believes it. Perhaps he and his advisers actually believe they could get away with it - now that the Republicans control the Supreme Court.