Larry Kudlow used to believe in immigration reform.

Then he swilled the Kool-Aid being served up by the likes of Donald Trump.

Kudlow, in a National Review column, has posited a profoundly preposterous notion. He wants a nation built by immigrants to slam the door shut — temporarily, he says — on all future immigrants. Anyone coming here in search of a better life need to look elsewhere, he says.

Kudlow believes the nation needs to enact what he called a “wartime lockdown” while we fight the Islamic State and other terrorists.

The term “un-American” only begins to define, in my view, the outrageousness of such a proposal.

“There may be some unfairness to this. But I don’t care,” wrote Kudlow. “Wars breed unfairness, just as they breed collateral damage. We may set back tourism. We may anger Saudi princes whose kids are in American schools. But so be it. We need a wartime footing if we are going to protect the American homeland.”

Saudi princes aren’t the only folks we’d offend. How about offshore business tycoons who want to send their young executives here to set up shop, to do business with American clients? How about folks from all corners of the planet seeking to come here because they read somewhere that America is “the land of opportunity”?

While we’re at it, Mr. Kudlow, let’s be sure to sandblast the inscription off the Statue of Liberty, the one that welcomes the “tired and the poor” to our shores. Hey, if not sandblast it — given that he says his idea is just temporary — we can hang a black shroud over it.

Kudlow has changed his mind on immigration reform because we’re now at war. I agree that we are at war. We’ve been at war since 9/11. Truth be told, we likely should have declared war on terrorists even before that. We’ve known for decades about the existence of terrorists willing to commit unspeakable acts.

The 9/11 attacks acted as the proverbial two-by-four between our eyes. The bad guys got our attention.

Do we shut down our borders, though, to become a nation none of us recognizes while we fight this international scourge? No.

If we are going to continue to be the world’s exceptional nation, then we keep our border open, welcome those who want to come here — while remaining hyper-vigilant in our quest to prevent terrorists from infiltrating us — and we keep taking the fight to the enemy.