In April, when the first reports about possible chemical weapons attacks in Syria came out, the Pew Research Center asked 1,003 people whether they would "favor military action against Syria if use of chemical weapons by Syria was confirmed." By a 14-point margin, a plurality of respondents said they would—45 percent yes, 31 percent no. Support was driven in part by Republicans, 56 percent of whom favored a strike on Syria.
Last week, as the Obama administration started issuing condemnations of Syria's chemical weapons use and bringing in members of Congress for briefings, Pew went back into the field and asked whether people favored "U.S. airstrikes against Syria." The story's changed entirely—by a 48-29 margin, respondents oppose the airstrikes. That's a 33-point swing against intervention. The highest level of support continues to come from Republicans, but that's fallen to 35 percent.
What happened? I think this chart's the most useful for our purposes.
Since April, Americans have seen Egypt turn on its revolutionary government and let the military reinstall itself as—they say!—a transitionary junta. Maybe that's had a role in this, because there's cynicism broadcast from every inch of this poll, from the mere 53 percent of people who think chemical weapons were used to the 54 percent of Republicans (!) who want the U.S. to "get a United Nations resolution to use force before taking military action," something that Russia and China will never allow.