More than 100,000 people have died in clashes between forces loyal to Assad and rebels trying to oust him from power over the past two and a half years. While Obama has repeatedly called for Assad to leave power, he has resisted calls for a robust U.S. intervention, and has largely limited American assistance to humanitarian aid. The president said last year that chemical weapons use would cross a "red line" and would likely change his calculus in deciding on a U.S. response.
Last week's attack in the Damascus suburbs is a challenge to Obama's credibility. He took little action after Assad used chemical weapons on a small scale earlier this year and risks signaling to countries like Iran that his administration does not follow through on its warnings.
Syrian activists say the Aug. 21 attack killed hundreds; the group Doctors Without Borders put the death toll at 355 people.
The U.S. Navy last week moved a fourth destroyer into the eastern Mediterranean. Each ship can launch ballistic missiles.
Officials said it was likely the targets of any cruise-missile attacks would be tied to the regime's ability to launch chemical weapons attacks. Possible targets would include weapons arsenals, command and control centers, radar and communications facilities, and other military headquarters. Less likely was a strike on a chemical weapons site because of the risk of releasing toxic gases.
Military experts and U.S. officials said Monday that the precision strikes would probably come during the night and target key military sites.
The president has ruled out putting American troops on the ground in Syria and officials say they are not considering setting up a unilateral no-fly zone.
On Capitol Hill, bipartisan support for a military response appeared to be building, with some key lawmakers calling for targeted strikes. A spokesman for House Speaker John Boehner said the Ohio Republican had "preliminary communication" with White House officials about the situation in Syria and a potential American response.
It's unlikely that the U.S. would launch a strike against Syria while the United Nations team is still in the country. The administration may also try to time any strike around Obama's travel schedule — he's due to hold meetings in Sweden and Russia next week — in order to avoid having the commander in chief abroad when the U.S. launches military action.
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