What President Trump plans to change about birthright citizenship is a mystery. But his comment to a reporter on the subject sent the commentariat into a tizzy.

Some raised valid constitutional and legal objections. As House Speaker Paul Ryan, R-Wis., noted, “you cannot end birthright citizenship with an executive order,” and the Constitution does, broadly, prescribe citizenship for babies born in the U.S.

But Democrats and their media allies risk overreaching if they think the public agrees with their absolutist view on the matter. The question is, ought we to confer citizenship to every baby born here. We suspect that most people agree, as we do, that children born here to illegal immigrants and legal passers-through should not get citizenship automatically, but children born to permanent residents should.

Birthright citizenship is an idea that has been present in law from around the time of America's founding and was planted in the Constitution in the 14th Amendment, where its purpose was to grant citizenship to former slaves.

It’s an instance of American exceptionalism. “You can go to France to live and not become a Frenchman,” Ronald Reagan once said, quoting from a letter he received. “You can go to live in Germany or Turkey, and you won't become a German or a Turk.”

Europe is being torn apart politically and culturally because immigrants are not assimilated. Japan is dying because it doesn’t have immigrants. Those countries make it hard for someone born there to become a citizen. In France and much of Europe, the result is a bifurcated society and a permanent underclass of immigrants and their children.

It is just and in keeping with the spirit of America that if a couple migrates here legally to become Americans and live here, their children born here should be considered Americans too. Children of lawful permanent residents should be treated from day one the same way as the children of citizens.

That's the easy part, and after setting that aside as obvious, the case for birthright citizenship as a policy matter, rather than as a constitutional one, gets much weaker. Why should someone be a citizen just because they happened to be born here to parents who were visiting the U.S.? Such a law encourages birth tourism and illegal immigration.

A mother with a tourist or student visa can come here and have a baby, acquiring American citizenship for her child, and then via her child for herself. If that mother is on a legal path to citizenship, that’s fitting. But if the U.S. birth is an accident of timing, or a gaming of the system through birth tourism, there is no excuse for it.

"[I]n America’s Chinese enclaves,” the Los Angeles Times reported in 2016, birth tourists “find a cottage industry of Chinese midwives, drivers and doctors who accept cash and ‘maternity hotels’ — apartments or homes run as hotels for the women during their pregnancies.”

Certainly, illegal immigrants shouldn’t win citizenship for their children because they managed to sneak in and give birth here.

On the question of parents illegally in the country, there’s a good argument the Constitution does not provide birthright citizenship.

The constitutional issues on children born to other visitors to the U.S. are more complicated — surely too complicated for the president to resolve with an executive order. But as a matter of policy, the U.S. should have a more sensible position than it does now, comparable to those of most other countries, which prevent foreigners from essentially stealing that precious commodity that is the proudest boast of citizens: "I'm an American."