Welcome to the Islamic Scare era, in which the nation becomes engulfed in a Donald Trump-induced fear of embedded Muslims planning terrorist attacks against the homeland. The United States has been through a phase like this before.

It was called the Red Scare, and we are all the poorer because of it.

The Red Scare, generated post-World Wars I and II, set off a chain of nasty behavior and excesses that trampled civil liberties and the freedoms we were taught to cherish. To be sure, there were American communists in the ’40s and ’50s who advocated the overthrow of the U.S. government and who worked as spies for the Soviet Union. The record of convictions is there to prove it.

But so, too, is evidence of the damaging effect that the Red Scare had on this country — lives turned upside down by false accusations and blacklists; political repression that walked all over freedom of expression and association.

A climate of fear can do that to a country.

Which is where we are now.

To hear Trump tell it, a large number of our Muslim neighbors believe violence against the United States is justified. To support that charge, Trump points to an online poll by the Center for Security Policy, a conservative think tank — a poll which, by the way, Post political reporter Philip Bump examined and described as “questionable.” The center’s poll estimates that 25 percent of adult Muslims in the United States, roughly 450,000, couldn’t care less if this country is bloodied by terrorist attacks.

Trump points to the mass murders carried out in San Bernardino, Calif., by a radicalized Muslim husband-and-wife team as evidence of the kind of danger that lurks within.

In a statement to reporters Monday, Trump said, “Without looking at the various polling data, it is obvious to anybody the hatred is beyond comprehension. Where this hatred comes from and why, we will have to determine. Until we [do] . . . our country cannot be the victims of horrendous attacks by people that believe only in Jihad.” He would impose a “total and complete shutdown” of Muslims entering the United States, would order the surveillance of “certain mosques” and would not even rule out creating a database on all Muslims.

Echoes of the Red Scare.

The now-defunct House Committee on Un-American Activities, and the late senator Joe McCarthy and FBI director J. Edgar Hoover, sounded similar alarms about the threat posed to U.S. security by a fifth column of secret American sympathizers of the Soviet enemy.

The anti-communists, in their fervor, set out to do something about it. To hell with free speech and the rights of those they slimed. And a wing of the U.S. government joined in, providing a road map for patriotic, God-fearing Americans to follow in protecting the country.

A 1950s Armed Forces Information film on h ow to spot a communist offered a fearful public some clues. “If a person consistently reads and advocates the views expressed in a communist publication, he may be a communist. If a person supports organizations, which reflect communist teachings, or organizations labeled communist by the Department of Justice, she may be a communist. If a person defends the activities of communist nations while consistently attacking the domestic and foreign policy of the United States, she may be a communist.

“If he does all these things over a period of time, he must be a communist.”

In 1955, the Army published a pamphlet, “How to Spot a Communist,” that was rescinded after protest by the American Civil Liberties Union.

And with good reason.

Conceding that there was “no fool-proof system in spotting a communist,” the Army pamphlet reassured the public that “fortunately, indications may give him away.”

What to look for?

Language used more frequently by communists than by the general public, such as: comrade, hootenanny, chauvinism, bourgeois-nationalism, colonialism, progressive, witch-hunt, reactionary.

Communists give themselves away when they talk about “violation of civil rights,” “racial or religious discrimination,” “immigration laws” or “peace.”

The sentiment of the time?

“You cannot trust your neighbors, or even next of kin. If mommy is a Commie then you gotta turn her in.” (Thanks, Chad Mitchell Trio.)

What will be Trump’s next phase with the Islamic Scare? Lessons on how to spot a jihadist? “Be on the lookout for bearded men robed in thobes, abaya-covered women and frequenters of mosques.”

Why not? The demagogic Donald Trump’s fear-mongering clearly knows no bounds.

Read more from Colbert King’s archive.