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Editor’s Note: Peter Bergen is CNN’s national security analyst, a vice president at New America and a professor of practice at Arizona State University.

(CNN) —  

The caravan of some 7,500 migrants wending its way north through Mexico is a political gift to President Donald Trump, who ran successfully on a get-tough on immigration and terrorism platform during his presidential campaign.

Peter Bergen
CNN
Peter Bergen

Trump tweeted Monday that there are “unknown Middle Easterners mixed” in with the thousands of migrants. The intent of this tweet is surely to play on American fears about the possibility of mysterious Middle Easterners attacking the country, as they did on 9/11.

There is just one problem with this notion: Every lethal terrorist attack in the United States since 9/11 has been carried out by a US citizen or legal resident, according to New America, a research institution that tracks jihadist terrorism cases.

In addition, of the more than 400 jihadist terrorist cases prosecuted in the United States in the past 17 years, not one of the terrorists infiltrated the country across the southern border, according to New America’s research.

Of course, the notion of a terrorist joining a caravan of migrants who are being filmed continuously for a matter of weeks is implausible on its face.

Since 9/11, three foreign terrorist organizations have mounted serious plots to attack the United States, and all the plotters flew into the country from South Asia and the Middle East. None of them crossed over the US-Mexico border.

Najibullah Zazi was trained by al Qaeda to blow up bombs in the Manhattan subway in 2009. He arrived in the United States from Pakistan by plane.

So too did Faisal Shahzad, whom the Pakistani Taliban trained to blow up a bomb in Manhattan a year later. Neither plot succeeded.

“Underwear bomber” Umar Farouk AbdulMutallab flew into the country on Christmas Day 2009 on the plane that he tried unsuccessfully to blow up over Detroit. Al Qaeda in Yemen had trained him.

The only cross-border infiltration by a terrorist was almost two decades ago when Ahmed Ressam, an Algerian, was arrested on a ferry arriving in Washington state from Canada on December 14, 1999. As Ressam’s car rolled out of the ferry, a US customs inspector pulled him over. Agents found 130 pounds of explosives in Ressam’s car. Ressam planned to bomb Los Angeles International Airport.

Despite the Ressam case, fomenting fears of terrorists crossing the border from Canada hasn’t gained much political traction in the United States.

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The view that terrorists are streaming across the southern border, however, is not uncommon among Trump supporters, not least retired Lt. Gen. Michael Flynn, who was Trump’s first national security adviser and who claimed in an August 2016 interview that there were Arabic signs along the US-Mexico border to guide potential terrorists into the States.

Flynn said, “I have personally seen the photos of the signage along those paths that are in Arabic. They’re like waypoints along that path as you come in. Primarily, in this case the one that I saw was in Texas and it’s literally, it’s like signs, that say, in Arabic, ‘This way, move to this point.’ It’s unbelievable.”

It was unbelievable, of course, because it was totally false.

So too is the canard that Mexico is a hotbed of jihadist terrorism, but that is not going to get in the way of Trump trying to make this an issue as the midterm elections draw closer.