The terrorist (I’m not using names here) who rammed his car into pedestrians on Westminster Bridge and ran it through the fence around the Houses of Parliament turns out to be a son of immigrants and was born in England: a second-generation terrorist. He’s not the only one: second-generation terrorists include, according to an interesting analysis by Stephen Dinan in the Washington Times, the June 2016 Orlando Pulse nightclub murderer, the son of immigrants from Pakistan, one of the December 2015 San Bernardino shooters, the son of immigrants from Pakistan; one of the attackers in a May 2015 Garland, Texas, Muhammad cartoon drawing contest, the son of immigrants from Pakistan; the November 2009 Fort Hood assailant (classified as a perpetrator of “workplace violence” by the Obama administration), the son of Palestinian immigrants; the two terrorist bombers at the April 2013 Boston Marathon bombing, the sons of asylum seekers from the Chechnya province of Russia.

Opponents of restrictions on numbers of immigrants, refugees and asylum seekers from predominantly Muslim countries frequently make the argument that such restrictions wouldn’t have kept these second-generation terrorists out of the nations where they committed their terrorist acts. That’s true. But it’s also true that if such restrictions had been applied to their parents when they sought to immigrate or sought refugee or asylum status, the second-generation terrorists wouldn’t be here either. This doesn’t settle the debate over whether we should block entry to people from countries where Islamist terrorism is common or to people from such countries who cannot be vetted. You can make serious arguments on both sides. But the phenomenon of frequent second-generation terrorism is something to weigh in the balance.