REP. TOM TANCREDO (R-Colo.) has a bold idea to stop illegal immigration: Deny automatic citizenship to the children of undocumented immigrants. "There is general agreement about the fact that citizenship in this country should not be bestowed on people who are children of folks who come into this country illegally," he told the Washington Times. General agreement? Perhaps among Mr. Tancredo's friends in the House but not among the framers of the 14th Amendment. Indeed, any such modern consensus would have a small problem in the text of the Constitution, which is, inconveniently for anti-immigrant demagogues, not subtle on the point. The 14th Amendment begins: "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." Not "all persons except children of illegal immigrants," not "all persons except those Congress exempts in moments of nativism." All persons.

How does Mr. Tancredo propose to get around this language? Like diplomats, illegal immigrants are not truly subject to American jurisdiction, he contends, and their children therefore don't satisfy the constitutional test for birthright citizenship.

The Supreme Court rejected this thesis more than a century ago. "Every citizen or subject of another country, while domiciled here, is within the allegiance and the protection, and consequently subject to the jurisdiction, of the United States," the court wrote. Diplomats, as a consequence of the lack of jurisdiction Mr. Tancredo would extend to aliens, cannot be arrested or charged with crimes. Is that what Mr. Tancredo has in mind for illegal immigrants? Members of Congress ought not follow him on this ugly and fruitless path.