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

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.

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