Syria's conflict is the most violent to emerge from last year's Arab Spring. Activists say at least 23,000 people have died over the last 18 months.
Obama wants Syrian President Bashar Assad to leave power. But he won't use U.S. military force to make that happen.
Romney says "more assertive" U.S. tactics are needed, without fully spelling them out.
The future of Arab democracy could hinge on the crisis. After dictatorships fell in Tunisia, Egypt, Libya and Yemen, critics say Assad's government has resorted to torture and mass killings to stay in power.
Its success would deny the U.S. a major strategic victory. Assad long has helped Iran aid Hamas and Hezbollah, destabilizing Lebanon while threatening Israel's security and U.S. interests in the Middle East.
But extremists among the opposition, Assad's weapons of mass destruction and worries about Israel's border security have policymakers wary about deeper involvement.
An FSA soldier walks through a street in Amariya district in Aleppo, Syria, Monday, Sept. 10, 2012. Syria's most prominent defector said in an interview that aired Monday that he opposes any foreign military intervention in the country's civil war and that he is confident the opposition can topple President Bashar Assad's regime. But Manaf Tlass, a Syrian general who was the first member of Assad's inner circle to join the opposition, said the rebels need weapons. (AP Photo/ Manu Brabo)