The louder liberals talk about some ancient constitutional right, the surer you should be that it was invented in the last few decades.

Democrats act as if the right to run across the border when you’re 8 1/2 months pregnant, give birth in a U.S. hospital and then immediately start collecting welfare was exactly what our forebears had in mind, a sacred constitutional right, as old as the 14th Amendment itself.

The louder liberals talk about some ancient constitutional right, the surer you should be that it was invented in the last few decades.

In fact, this alleged right derives only from a footnote slyly slipped into a Supreme Court opinion by Justice Brennan in 1982. You might say it snuck in when no one was looking, and now we have to let it stay.

The 14th Amendment was added after the Civil War in order to overrule the Supreme Court’s Dred Scott decision, which had held that black slaves were not citizens of the United States. The precise purpose of the amendment was to stop sleazy Southern states from denying citizenship rights to newly freed slaves — many of whom had roots in this country longer than a lot of white people.

The amendment guaranteed that freed slaves would have all the privileges of citizenship by providing: “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 drafters of the 14th amendment had no intention of conferring citizenship on the children of aliens who happened to be born in the U.S. (For my younger readers, back in those days, people cleaned their own houses and raised their own kids.)

Inasmuch as America was not the massive welfare state operating as a magnet for malingerers, frauds and cheats that it is today, it’s amazing the drafters even considered the amendment’s effect on the children of aliens.

But they did.

The very author of the citizenship clause, Sen. Jacob Howard of Michigan, expressly said: “This will not, of course, include persons born in the United States who are foreigners, aliens, who belong to the families of ambassadors or foreign ministers.”

In the 1884 case Elk v. Wilkins, the Supreme Court ruled that the 14th Amendment did not even confer citizenship on Indians — because they were subject to tribal jurisdiction, not U.S. jurisdiction.

For a hundred years, that was how it stood, with only one case adding the caveat that children born to LEGAL permanent residents of the U.S., gainfully employed, and who were not employed by a foreign government would also be deemed citizens under the 14th Amendment. (United States v. Wong Kim Ark, 1898.)

And then, out of the blue in 1982, Justice Brennan slipped a footnote into his 5-4 opinion in Plyler v. Doe, asserting that “no plausible distinction with respect to Fourteenth Amendment ‘jurisdiction’ can be drawn between resident aliens whose entry into the United States was lawful, and resident aliens whose entry was unlawful.” (Other than the part about one being lawful and the other not.)

Brennan’s authority for this lunatic statement was that it appeared in a 1912 book written by Clement L. Bouve. (Yes, THE Clement L. Bouve — the one you’ve heard so much about over the years.) Bouve was not a senator, not an elected official, certainly not a judge — just some guy who wrote a book.

So on one hand we have the history, the objective, the author’s intent and 100 years of history of the 14th Amendment, which says that the 14th Amendment does not confer citizenship on children born to illegal immigrants.

On the other hand, we have a random outburst by some guy named Clement — who, I’m guessing, was too cheap to hire an American housekeeper.

Any half-wit, including Clement L. Bouve, could conjure up a raft of such “plausible distinction(s)” before breakfast. Among them: Legal immigrants have been checked for subversive ties, contagious diseases, and have some qualification to be here other than “lives within walking distance.”

But most important, Americans have a right to decide, as the people of other countries do, who becomes a citizen.

Combine Justice Brennan’s footnote with America’s ludicrously generous welfare policies, and you end up with a bankrupt country.

Consider the story of one family of illegal immigrants described in the Spring 2005 Journal of American Physicians and Surgeons:

“Cristobal Silverio came illegally from Oxtotilan, Mexico, in 1997 and brought his wife Felipa, plus three children aged 19, 12 and 8. Felipa … gave birth to a new daughter, her anchor baby, named Flor. Flor was premature, spent three months in the neonatal incubator, and cost San Joaquin Hospital more than $300,000. Meanwhile, (Felipa’s 19-year-old daughter) Lourdes plus her illegal alien husband produced their own anchor baby, Esmeralda. Grandma Felipa created a second anchor baby, Cristian. … The two Silverio anchor babies generate $1,000 per month in public welfare funding. Flor gets $600 per month for asthma. Healthy Cristian gets $400. Cristobal and Felipa last year earned $18,000 picking fruit. Flor and Cristian were paid $12,000 for being anchor babies.”

In the Silverios’ munificent new hometown of Stockton, Calif., 70 percent of the 2,300 babies born in 2003 in the San Joaquin General Hospital were anchor babies. As of this month, Stockton is $23 million in the hole.

It’s bad enough to be governed by 5-4 decisions written by liberal judicial activists. In the case of “anchor babies,” America is being governed by Brennan’s 1982 footnote.