AP Photo

Unusual for a Democratic president, Barack Obama holds a huge lead when likely voters are asked which candidate would best handle foreign affairs. At present he enjoys a 12-point lead over Mitt Romney on foreign policy, according to the latest CNN/ORC survey of likely voters.

But that poll was released days before militants scaled the walls of the U.S. embassy in Cairo, and before what Secretary of State Hillary Clinton calls a “small, savage” group attacked the U.S. consulate in Benghazi, Libya with rockets and guns. The U.S. ambassador, J. Christopher Stevens, and three other diplomats died in that assault on American sovereignty. The televised images of extremists joyfully tearing up an American flag—taken from the Cairo embassy—may drive down Obama’s perceived...