Republican presidential candidate Ben Carson on Monday recalled the men who orchestrated the bombing at the Boston Marathon to argue that the U.S. should not accept emergency refugees fleeing Syria. The retired neurosurgeon, who is recently earning silver medals in national opinion polls, raised the specter of Tamerlan and Dzokhar Tsarnaev, the immigrant brothers who came to the United States in 2002 and a decade later organized the attack. Carson said the U.S. had not substantively improved how immigrants those like the brothers were vetted when they came as refugees from Kyrgyzstan. “How did that screening process work for the Tsarnaev Brothers?” Carson told CNN’s John Berman on “The Lead.” “We don’t know whose those people are, and the majority of them are young males, and they could easily be people who could be infiltrated by terrorists.” Carson said it was all too easy for Islamic militants to take advantage of the relaxed standards for refugees. “If I was ISIS, if I were the global jihadists, and I knew the United States was about to take in 10,000 or 65,000 or 100,00 people from my region, I would infiltrate them with my people,” he said. The presidential candidate also continued to back away from a fight he said he mistakenly walked into with GOP rival Donald Trump, who is the only Republican leading Carson in most of these national surveys. A week after Carson seemed to suggest that he did not think Trump, a New York businessman who is not known for strong religious affectations, did not live a faith-driven life, Carson reiterated that his comments had been misconstrued. “Everybody operates on the basis of faith – it may not be faith in God, it may be faith in themselves or some other entity – but there is n one whose demeanor and relationships with others is not dictated by their faith,” he said. Carson also characterized his position on immigration as “probably not that far away” from Trump’s, despite having disagreed with Trump on the viability of deportations of undocumented immigrants.