To believe his critics, Donald Trump has ripped up the U.S. Constitution and sprinkled its shreds on the smoldering embers of what was once the Statute of Liberty.

He did this, of course, by proposing a temporary ban on Muslim immigration into the United States, which might be the most roundly and fiercely denounced idea in America since the British Parliament passed the Intolerable Acts (in 1774).

There is no doubt about it: Donald Trump’s proposal is invidious; not all Muslims are a security risk. It is unworkable; among other things, airlines would have to screen travelers from Europe for their religion. It is imprudent; we don’t want to send a message of generalized hostility to Muslims.

But it’s not unconstitutional. Trump’s detractors, and even some of his fellow Republicans, can’t help making this charge, even though it betrays a misunderstanding, not just of the Constitution, but of the very nature of a sovereign nation.

“We do not discriminate on people based on religion,” Ben Carson said in response to Trump’s proposal, “that’s constitutional, that’s in the First Amendment.” Of course, he’s right. Except the First Amendment isn’t a free-floating grant of rights to all of mankind.

We are a sovereign country with the right to exclude whomever we want from coming here. In keeping with this basic attribute of nationhood, a long line of Supreme Court cases have upheld the “plenary power” of the political branches to set immigration policy in any way they please.

As Jan Ting of Temple University notes, the Supreme Court wrote in a 1977 opinion, “Our cases ‘have long recognized the power to expel or exclude aliens as a fundamental sovereign attribute exercised by the Government’s political departments largely immune from judicial control.'” The court remarked that “Congress regularly makes rules that would be unacceptable if applied to citizens.”

We have seen exercises of this plenary power in recent decades. During the hostage crisis, as FrontPage Magazine reported, Jimmy Carter ordered that all nonimmigrant visas from Iran be invalidated and that no more be issued, absent a compelling humanitarian reason. He also mandated that Iranian students in the United States report to the authorities, who queried them about potential radical sympathies. Some students were expelled. Jimmy Carter has not heretofore been known for his fascistic tendencies.

On a much smaller scale, the Obama administration paused the Iraq refugee resettlement program in 2011 after it came to light it had welcomed two terrorists into the United States.

Obviously, these comparisons aren’t quite apt. As policy responses, they were more narrowly targeted and directly related to a threat than Trump’s blunderbuss reaction to San Bernardino.

It is different, and less disturbing, to target the nationality of potential entrants, rather than their religion. It is the difference between Trump proposing, say, a temporary moratorium on visas for people coming here from Pakistan and Saudi Arabia — San Bernardino terrorist Tashfeen Malik was a Pakistani who spent a lot of time in Saudi Arabia — and a halt to all Muslims. Trump’s ban would apply to an Iraqi interpreter who worked alongside U.S. troops, as well as to a harmless Ph.D. from Malaysia.

Still, the braying about the First Amendment from the left is rich. The implicit position of Trump’s progressive critics is that the First Amendment doesn’t protect all political speech, or cover people with religious objections to gay marriage, or prevent the Obama administration from forcing nuns to sign up for contraception coverage, but it extends to foreigners hoping to gain entry into the United States.

The embedded assumption is that migrating here is some sort of global civil right. Republicans, too, are subject to this hazy thinking. Trump may be ignorant and bombastic, but his supporters believe that, if nothing else, he understands that the security and interests of Americans must come first. They know no such thing about his hysterical detractors.

Rich Lowry is a syndicated columnist. He can be reached via e-mail at: comments.lowry@nationalreview.com.