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Trump has a shoddy grasp of the Constitution.

One day after saying he could reinterpret the Fourteenth Amendment’s Citizenship Clause by executive order to eliminate birthright citizenship, the president doubled down on the issue on Twitter.

The tweet is a Russian nesting doll of falsehoods. Birthright citizenship does not cost the United States “billions of dollars,” nor is it “very unfair” to the citizens whose rights it protects. Whether it will be ended “one way or the other” is also debatable: A constitutional amendment has little hope of ratification, and the Supreme Court would likely reject an effort to re-interpret the clause more narrowly. After all, the clause effectively overturned Dred Scott v. Sandford, the worst decision in the court’s history.

The real humdinger in Trump’s tweet, however, pertains to the phrase “subject to the jurisdiction.” The Fourteenth Amendment reads, “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.” The president doesn’t explicitly name undocumented immigrants, but it seems he’s arguing that they are not “subject to the jurisdiction” of the U.S. As I noted in article this morning, most legal scholars argue otherwise. After all, the Justice Department regularly charges undocumented immigrants with crimes and deports them under the authority of the U.S.

Trump is free to personally disagree, of course. But if he thinks he’s right, he’d first have to grant the nation’s undocumented population something akin to diplomatic immunity—a move that he and his supporters may not be able to stomach.