Read: Trump’s reality show in the Oval Office

Trump’s “10 terrorists” claim is drawn from Department of Homeland Security statistics from last year. The figures stated that an average of 10 individuals a day who showed up on terrorist watch lists were prevented from entering the United States by land, sea, or air. The numbers the president invoked to insist again on a wall at the southern border refer to stops at all borders—and they also show that the post-9/11 screening systems are likely already preventing suspected terrorists from entering the country.

Trump was drawing the connection between immigration and terrorism well before the migrant caravan became an issue. In the summer of 2016, shortly after Omar Mateen killed 49 people at a gay nightclub in Orlando in an attack that the Islamic State claimed responsibility for, Trump delivered a speech on “immigration, terrorism, and national security.”

Mateen was born in New York State after his parents left Afghanistan for the United States. Still, the then-candidate Trump said, “the bottom line is that the only reason the killer was in America in the first place was because we allowed his family to come here.” He went on: “We are importing radical Islamic terrorism into the West through a failed immigration system.”

The logic made a kind of intuitive sense. The perpetrators of the worst terrorist attack the United States has ever seen, which killed nearly 3,000 people on September 11, 2001, were all Middle Eastern nationals, most of them on tourist visas. As Trump also noted in his speech, the Boston Marathon bombers had received asylum in the United States.

Is there actually a link between immigration and Islamist terrorism, though? Since 9/11, numerous studies have found the terrorist threat to the U.S. to be largely homegrown. New America, for example, observed in September, “Every jihadist who conducted a lethal attack inside the United States since 9/11 was a citizen or legal resident.” In the think tank’s database of people either charged with committing or killed while committing jihadist crimes in the U.S. from 2001 to 2018, 84 percent were citizens or permanent residents.

Read: Where America’s terrorists actually come from

This is largely because terrorism is rare in general. But it is also partly a function of George W. Bush–era immigration and border-security efforts. The authors of the “9/11 Commission Report” observed in 2010, “In the decade before September 11, 2001, border security—encompassing travel, entry, and immigration—was not seen as a national security matter,” and “Al-Qaeda had been systematically but detectably exploiting weaknesses in our border security since the early 1990s.” After those attacks, the administration threw billions of dollars at border security, dramatically tightened visa screening, made passports more secure, and instituted systems for gathering information about travelers before they reached the United States.