President Trump is making a blunder with his vow to end birthright citizenship. He’d compound the error were he to try to snuff out this constitutional beacon with a mere executive order.

I say that not out of hostility to the president. On the contrary, The New York Sun endorsed him (and I voted for him) and agree with most of his major policies, including enforcing our immigration laws.

Yet it’s hard to see the logic of curbing legal citizens, which is what ending birthright citizenship would be doing. Our long-term economic problem could yet be lack of enough people.

Mr. Trump’s vow to end birthright citizenship — and to do so by executive order — was made in an interview with the online publication Axios. It is due to be broadcast on Sunday.

“We’re the only country in the world where a person comes in and has a baby, and the baby is essentially a citizen of the United States . . . with all of those benefits,” an Axio squib quoted Mr. Trump as saying. “It’s ridiculous,” Mr. Trump said, “and it has to end.”

Actually, the Harvard Human Rights Journal reckons that there are at least 30 countries with automatic birthright citizenship. Even were we the only one, the 14th Amendment wouldn’t be ridiculous.

It is a response to the Supreme Court’s Dred Scott decision. That was the pre-Civil War ruling that a black person whose ancestors were brought here in bondage could never be a citizen.

After the war, America ratified the 14th amendment. It said that “all persons born or naturalized in the United States” and subject to its jurisdiction are citizens of the US and of the state where they reside.

The amendment left in place the Constitution’s grant to Congress of the power to pass a “uniform rule of naturalization.” It’s hard to see, though, how even Congress could nullify the 14th Amendment.

That’s fully part of the Constitution. It’s American bedrock. Congress echoed it — verbatim on the key point — when it passed its “uniform rule” in the Immigration and Nationality Act of 1952.

It’s even harder to see how Mr. Trump could get around it by executive order. Or why he would even want to go that route. It’s one of the things, after all, that got President Obama into trouble.

That was when Mr. Obama used an executive memo to defer action on childhood arrivals. Not even Mr. Obama, though, sought to overturn the Constitution by executive order. He was just dodging Congress.

Recently, two scholars brought out an article in National Affairs questioning the assumption that a child born here is a “birthright citizen regardless of the parent’s legal status.”

They also dispute that such citizenship “is required and guaranteed by the Constitution.” Yet not even those two scholars — Peter Schuck and Rogers Smith — suggest the president can waive the matter with an executive order.

Instead, they reckon that it’s a matter “for Congress and the American people to resolve.” They cannily predicted that Mr. Trump, who campaigned against birthright citizenship, would eventually take it up.

There are scholars, such as Michael Anton of Hillsdale College, who reckon that Mr. Trump just might prevail by executive order. He’d press in court the argument that the 14th Amendment applies mainly to freed slaves.

My own view is that curbing birthright citizenship conflicts with Mr. Trump’s stated core values. One is that he’s pro-life, which means that he understands the concept of human capital.

That principle holds that people are innately valuable. More people create more wealth and are in themselves good. Our major religions believe this. As do our greatest economists.

As did the American revolutionaries.

One reason they seceded from England was that George III was obstructing immigration. He had, the Declaration of Independence complained, “endeavoured to prevent the population of these states.”

It’s not my intention to suggest we have no problems even with birthright citizens. Yet surely it is the obligation of leaders to get Congress to address problems without casting out children born here.

Birthright citizenship fits well with Mr. Trump’s view of capitalism. He comprehends that if taxes and regulations are cut, the economy can expand for decades.

To get long-term growth right, we’ll need all the help we can get.

From the New York Post.