The end game in this confrontation has always been Iran. Iran has let her mouth overload her butt, with threats and pledges of soldiers - which would only have to come from the Becka Valley in Lebanon.
Taking down Iran is a major goal, since 1979 for the US. The major problems are that Iran has spent years doing recon missions on US Missions abroad and they will attack them, just as they did in 1979. The problem for the US then is to bait Iran into attacking another US Embassy or Consulate so that we have the pretext for direct war. Attacking an Annex denotes there is not actually a link to diplomacy but rather intelligence operations, so Benghazi while tragic does not trigger action against either Syria or Iran even if they were involved.
Iran will flushed out shortly, she can not much longer endure the sanctions, plus a major refinery or import terminal's destruction. Actually, the real key to Iran would be to cut off food imports, along with energy, but our EU Allies would stand to lose too much currency given the dependence those social welfare states have on dictators and the favorable trade terms.
My guess is that any build up for Syria is simply a diversion that the US hits Iran instead, while the Saudi's, UAE and French take on Syria. Assad's escape helo will probably be shot down by friendly forces.
Does Israel play an active role in any of this?