Al-Nusra has also learned from history, according to other Islamists among Syrian rebel ranks. Many of its more experienced fighters saw al Qaeda in Iraq alienate the Sunni tribes there with its vicious sectarian bloodletting. As Aaron Zelin of the Washington Institute for Near East Policy wrote in Foreign Policy last week, "Jabhat al-Nusra seems to have learned from the mistakes of al Qaeda in Iraq: It has not attacked civilians randomly, nor has it shown wanton disregard for human life by publicizing videos showing the beheading of its enemies."

Instead, Islamist leaders in Aleppo say, it is looking to broaden its appeal and spread its fundamentalist message.

Ordinary people in Aleppo complain that some FSA units mishandle or misappropriate bread distribution, and they have begun to look to Islamist groups for greater honesty in managing local affairs. One chant recently heard in Aleppo, revealingly, was this: "We don't want a thieving free army, we want an Islamic army."

The United States would rather see that role in the hands of the Local Coordination Committees, present in many Syrian cities since early in the uprising.

Such is the undercurrent of resentment toward the United States among Syrians pummeled by nearly two years of regime attacks that designating al-Nusra may have the unintended consequence of making it more popular. Designation may also make it more attractive to foreign jihadists. According to the SITE Intelligence Group, another jihadist group, the al-Sahaba Army, has already congratulated al-Nusra for its designation, describing it as a "great honor" and calling on other groups to rally to al-Nusra.

For now, the group has no formal affiliation with al Qaeda, and according to other Islamist fighters it is probably wary of being pigeonholed as part of the group, for fear of causing a backlash among a population that historically is among the less conservative in the Arab world.

One leading Islamist in Aleppo described al-Nusra as similar to jihadist groups in Iraq before they morphed into al Qaeda. So far, he said, al-Nusra has yet to receive al Qaeda's seal of approval.

The U.S. State Department thinks otherwise.