Most believe Assad is guilty of using chemical weapons; 53% say there is clear evidence that the Syrian government used them against civilians there while just 23% say there is no clear evidence of a chemical attack.
…but the public doesn’t believe the Obama administration’s arguments that limited strikes on Syria post little risk and wouldn’t lead to an extended engagement, or that they would dissuade Assad from further chemical attacks:
Three-quarters (74%) believe that U.S. airstrikes in Syria are likely to create a backlash against the United States and its allies in the region and 61% think it would be likely to lead to a long-term U.S. military commitment there. Meanwhile, just 33% believe airstrikes are likely to be effective in discouraging the use of chemical weapons; roughly half (51%) think they are not likely to achieve this goal.
So it would seem that if the administration wants to rally the public, the focus should be on less on persuading people that Assad is guilty of gassing his own people and more on persuading them that the response to it would have an impact and entails minimal risk.
By the way, just for the fun of it, I dug up an old Pew poll taken on the eve of the Iraq War. The public was far more accepting of the (Bush) administration’s case for Saddam’s guilt: Two thirds believed he had a hand in the September 11th attacks, and eight in 10 believed Iraq already had nukes or could soon obtain them. Meanwhile, significantly smaller percentages believed that attacking Iraq could have negative consequences (such as hurting the U.S.’s image among Muslims or leading to a large number of U.S. casualties) than now worry about the risks in attacking Syria outlined above.
Obviously there are numerous reasons the parallel is far from perfect, so this doesn’t really tell us much. But it is interesting to note the stark difference in public opinion climates, whether it’s because of war weariness, a more sophisticated public, or the difference in the amount of time that has passed since 9/11. People forget that Bush administration pushed for the vote on the Iraq War barely a year after the attacks. Exactly eight days from today, 12 years will have passed since them.