Director of National Intelligence James R. Clapper told members of Congress last week that Jabhat al-Nusra, an al-Qaeda aligned group in Syria, “does have aspirations for attacks on the homeland.” American and Egyptian officials expressed alarm this week at signs that Egyptians who fought in Syria have returned home to mount an insurgency.

Critics of Obama administration policy in Syria argue that none of this should come as a surprise. For years, they have predicted that Assad and his Iranian and Russian backers would fight tenaciously; militants would flock to Syria; and the region would be destabilized by refugee flows, rising sectarianism and radicalized fighters returning home.

“A lot of things that the pro-interventionist crowd had argued two years ago have come to pass,” said Shadi Hamid, a Brookings Institution expert who called for military intervention in 2012. “The argument was that radicalism will rise.”