More generally, there does not appear to be empirical evidence backing the claim that refugees pose a particular domestic terror threat. The Boston Marathon bombers, Tamerlan and Dzhokar Tsarnaev, are frequently cited as evidence that it only takes a few radicalized individuals to slip through the cracks of U.S. security vetting — but the Tsarnaevs are believed to have radicalized after they arrived in the U.S. They also entered on a tourist visa and received political asylum, meaning that they didn’t go through the painstaking process that will be conducted for every Syrian refugee before he or she ever boards a plane for the U.S.

According to the Migration Policy Institute, none of the 784,000 refugees the U.S. has resettled since 9/11 has been arrested on domestic terror charges, and only a handful have been arrested for aiding plots abroad. A recent New York Times analysis found that none of the "jihadist-inspired" terror attacks in the U.S. since, and including, 9/11 involved a refugee. Speaking about her native Canada, Stein noted that both high-profile terror attacks last year were carried out by Canadian citizens who were recent converts to Islam. “The message here is not that operatives are coming from Syria to attack Europeans or North Americans," she said. "There’s simply no evidence of that.”

Forgetting that it was Europeans behind the Paris attack could obscure another security risk, said U.S. Sen. John Barrasso: the visa-waiver program that allows citizens of 38 nations to enter the U.S. without pre-screening. While U.S. lawmakers debate over highly vetted Syrians, the more pressing concern could be that the French and Belgian citizens “involved in the attacks on Paris could have just gotten on a plane” to the U.S., Barrasso, a Republican from Wyoming, told reporters at a news conference in Halifax. That is why Sens. Diane Feinstein, D-Calif., and Jeff Flake, R-Ariz., are co-sponsoring a bill they say will patch loopholes in the visa-waiver program.

Nevertheless, wariness about Obama’s resettlement plan appears to be growing. According to a recent Bloomberg poll, 53 percent of Americans now support blocking the resettlement of Syrian refugees in the U.S. Meanwhile, the House of Representatives last week overwhelmingly passed an act to delay refugee resettlement, the American Security Against Foreign Enemies act. Speaker of the House Paul Ryan, R-Wisc., said the delay was necessary "until we can be certain no one coming here is a threat to our country," arguing that the situation in Syria was too murky to fully understand the threat an individual may pose. Once they return from the Thanksgiving holiday recess, the Senate will open debate on the bill.

Sen. Tim Kaine, D-Va., a critic of the bill who led a Senate delegation in Halifax, said he didn’t think it would pass in its current form. “Syrian and Iraq refugees are not ‘foreign enemies,’” Kaine said during one session in Halifax, referring to the act’s name. “We have an enemy, and the enemy is ISIL. Not the refugees fleeing from ISIL.” Even John McCain, R-Ariz., a hawkish voice in the Senate and vocal proponent of stronger military intervention against ISIL, has called his House colleagues’ focus on refugees “misplaced.”

Even so, experts note that the American public’s fear response to terror is to be expected. Paris, in particular, was discomforting to many Westerners, who had been under the impression that ISIL was focusing its efforts on territorial expansion in Syria and Iraq — not Al-Qaeda-style strikes abroad. The soft targets struck on Nov. 13th — restaurants, bars, a concert hall and stadium – were specifically chosen to make people feel unsafe in public spaces they visit on a daily basis.

“It evokes fear, and we need to understand that. It’s legitimate for people to feel frightened,” Stein said. “But the job for academic and political leaders is to bring the evidence to bear, and say, ‘We understand why you feel this way, but the evidence doesn’t support those fears.’”