In terms of military responses, Assad could launch rockets at U.S. allies Turkey, Jordan or Israel. But that could touch off a prolonged military engagement with an outside power at a time when the regime is already in a bloody fight for its survival.
An attack against NATO-member Turkey could trigger a response from the entire military alliance, while Jordan hosts about a dozen U.S. F-16 jets, a Patriot missile battery and around 1,000 American troops.
As for Israel, the Assad regime could launch rockets at the Jewish state, or turn to Hezbollah to do so. The militant group, which fought Israel to a standstill in a 34-day war in 2006, is believed to have a well-stocked arsenal of missiles capable of hitting the country's major cities.
But analysts say Syria is unlikely to pursue such a course unless the U.S. strikes pose an immediate threat to Assad's grip on power.
Hezbollah would have a lot to lose. The group is already facing flak at home for fighting alongside Syrian government troops against the rebels. A full-on confrontation with Israel on behalf of Syria would probably be a tough sell to its Shiite constituents at home, let alone the broader Lebanese public.
"I can't see a situation whereby they would accept an order from Assad to, say, attack Israel or attack some domestic enemies. I think that would be too damaging for their position," said Chris Phillips, a Syria specialist at Queen Mary University in London.
Israeli defense officials also say the odds of retaliation by Syria or Hezbollah are very low. Still, Israel has deployed Iron Dome anti-missile batteries in the Tel Aviv area and toward its northern frontier with Syria.
Between these two extremes lies a middle path for Assad, which would involve an attack such as a car bombing carried out by a sympathetic militant group.
"Something to indicate to the outside world that it's dangerous to mess with the Assad regime, that they have levers that can cause damage elsewhere, while also plausibly denying that they've had direct impact," Phillips said.
As an example, Phillips pointed to a double car bombing earlier this year in Turkey that killed more than 50 people. Turkey blames Syria, while Syria denies any role.
Associated Press writer Lolita C. Baldor in Washington contributed to this story.
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