From CNN:

Director of National Intelligence James Clapper testified last week in front of the Senate Intelligence committee that the al Qaeda tied group in Syria, al-Nusra Front, has “aspirations” for attacks in the U.S. How real is the threat that these groups have capabilities to attack here in the U.S.? “One of the highest security threats you can think of…is the fact that we have jihadists training in Syria that could come back to the homeland with legal travel documents, and perpetrate an act of terrorism in the homeland,” House Homeland Security Chair Rep. Michael McCaul told CNN’s “The Lead with Jake Tapper.”