How could the President proceed without offending Congress? Either he is weak because Congress needs to act and won't, or he is a dictator because he leads and Congress won't follow.
If congress is so concerned about the Syrians and terrorist, let them make the declaration of war against the parties, allocate funds and scope of the conflict, like the constitution requires.
Congress will also have to negotiate the mine field of the Arab politics to get approval for such a war. How will the Saudis frame the optics of approving the use of American (or Western / non Muslim troops) killing very conservative Muslims, in their own country, when these conservatives have done nothing wrong (according to their interpretation of the Koran)? How will the Gulf State rulers keep the man on the Arab streets from revolting against them for their approval of the use of US troops to kill Muslims, and how will the Gulf State rulers stay in power, considering that the Arab Spring has just happened. If the Gulf State rulers fall, like in Egypt and Libya, then you have a very significant problem on your hands.
When are the Saudis and Gulf States going to step up and take responsibility for their regional security, or when are we going to make the accountable for their own security? There are a great many Saudis that have nothing better to do but to plan and train for terrorist missions. Going to war will give these men something to do, other than planning to kill US citizens, and simultaneously help the Saudis thin their herd, instead of thinning ours.