The Bastille Day slaughter of 84 people in Nice, following the 130 killed in Paris on May 13, 2015, left France the victim of two of the largest terrorist attacks outside the Middle East.

In France—as in the U.S., Turkey and Bangladesh—such attacks have nearly all been instigated by homegrown terrorists, not recent immigrants. All known Paris attackers were citizens of France or Belgium. The killer in Nice, Mohamed Lahouaiej Bouhlel, was a resident of France since 2005.

The New America Foundation counts 94 Americans killed in seven Islamic terrorist incidents since 9/11. Terrorists in Orlando, San Bernardino, Fort Hood, Seattle and Little Rock were born in the USA; those in Boston and Chattanooga had been citizens for decades. 

The House Homeland Security Committee reported that, “Since September 11, 2001, there have been 124 U.S. terrorist cases involving homegrown violent Jihadists.”

Yet despite the homegrown origin of Jihadist terrorism, American politics has somehow spun toward the notion that controlling terrorism is primarily a matter of controlling immigration.

As Donald Trump put it, “We’re importing radical Islamic terrorism into the West through a failed immigration system.” He first proposed to bar immigrants who identify themselves as Muslims, then to “suspend immigration from areas of the world where there’s a proven history of terrorism against the United States, Europe or our allies” (a definition broad enough to include France).

One problem with focusing on newly arriving Muslims is that many U.S. terrorists and sympathizers converted to Islam, like Little Rock shooter Carlos Bledsoe in 2009. Out of 87 Americans charged with ISIS-related offenses in the past three years, a George Washington University study found 38 percent were converted to Islam.

More important, if fear of foreigners is supposed to be the big hot-button issue, then immigration is almost beside the point. Immigrants account for much less than 1 percent of the foreigners who arrive in the United States each year.

Without counting immigrants or refugees, 180.5 million foreigners came to the United States in 2014, according to the Department of Homeland Security. That is more than four times larger than all the immigrants now living in the United States (42.4 million).

Nobody could possibly imagine it feasible to carefully vet or otherwise limit the millions of tourists, business travelers and students who are constantly coming to the United States. So, what accounts for all the anxiety about infinitely smaller numbers who arrive as immigrants?

In contrast with 180.5 million nonimmigrants arriving in 2014, only 69,975 arrived as refugees and only 481,392 new arrivals were granted green cards.

Any foreigner who wanted to come here on a suicidal terrorist mission needn’t wait two years to be vetted as a refugee, or try to get on a long waiting list for a green card. Tourists are allowed to stay in the U.S. for 90 days, business travelers 12 months, skilled workers six years, and students stay as long as they’re enrolled. Citizens of 38 “visa waiver” countries (including France and Belgium) don’t even need a visa.

The chances of Homeland Security missing a handful of potential terrorists among 180.5 million temporary visitors are surely much greater than the odds of missing them among a few thousand well-vetted refugees.

What about illegal immigrants? In “Estimates of the Unauthorized Immigrant Population,” Homeland Security concluded, “It is unlikely that the unauthorized immigrant population has increased since 2007.” Political obsession with the Mexican border is also misplaced because most foreigners arrive on airplanes or ships.

Foreign nationals have to fill out an I‑94 Arrival/​Departure form only if traveling by land, so we know that 105.6 million (58.5 percent) of the 180.5 million foreign visitors in 2014 came by airplane or ship. Eighty percent of the 74.9 million who instead crossed the Canadian and Mexican borders were tourists; the rest were mostly business travelers and students.

In short, refugees and immigrants add up to a tiny fraction of the 180.5 million foreigners who come to the United States quite legally in a typical year, and commonly remain for months or years. Nearly all Jihadist attacks in the West have been homegrown. But even if that were not the case, it is much faster and easier to come to the United States as a legal nonimmigrant than to do so as refugee or permanent resident.

The U.S. visa program may well need tighter rules and enforcement, but that is an entirely different issue than making refugees and immigrants the primary scapegoats of anti-terrorist strategy. Because resources available for domestic security are limited, “keeping us safe” requires devoting the most resources to the most probable dangers rather than turning to hypothetical long shots.

Thwarting terrorism is primarily a task for intelligence agencies and police. Combating ISIS is primarily a military issue. Immigration policy or refugee quotas may indeed be important for other reasons, but the alleged link to Jihadist/​Islamist terrorism is tenuous at best.

Attempting to enforce immigration restrictions based on a person’s self-described religious preference (or apparent national origin) would not be easy or cheap. Neither would tripling the size of the current 650-mile wall on the Mexican border. Such grandiose projects inevitably require diverting limited time and money away from more-promising options—such as hiring more FBI agents or private security firms for surveillance of suspicious activities and persons.