Half of U.S. attacks linked to Islamic extremism since 9/11 were committed by men born in the United States, according to the Times. Even the 9/11 attackers themselves were in the U.S. either on a tourist, student or work visa, suggesting that refugees pose less of a risk to national security than some politicians may think.
Since the Paris attacks, elected officials–mostly Republicans–have clamored to shut down or mitigate the flow of refugees from Syria into the U.S. Governors have threatened to block or expel refugees from their states and the House of Representatives passed legislation making it much more difficult for U.S. officials to admit Syrian refugees.
Applying for refugee status in the U.S. is a complicated and lengthy process that can stretch up to two years and involves multi-agency security checks and interviews. There are much easier ways to gain admittance to the country: shoe bomber Richard Reid, for example, was a British citizen who did not need a visa because of a visa-waiver program which allows citizens from some 38 countries to travel freely to the U.S.
Dzhokhar and Tamerlan Tsarnaev, the Boston Marathon bombers, were not refugees either. Their parents were asylum seekers, which differs from refugee status in that it requires a family or individual is already on U.S. soil. While Dzhokhar Tsarnaev is a naturalized citizen, his brother Tamerlan had a green card.