Rice: Failure to Act Could Make Arab Spring Take 'Even Darker and More Ominous Turn'

Stating the administration does "not assess that limited military strikes will unleash escalatory reactions in the region," National Security Adviser Susan Rice made the case for her boss' use of force authorization today at a Washington think tank.

"There's no denying what happened on Aug. 21," Rice said at the New America Foundation address, stressing that Bashar al-Assad's forces loaded chemical weapon payloads onto rockets that were fired into an opposition-controlled pocket of the Damascus suburbs.

"Innocent civilians were jolted awake, choking on poison; some never woke up at all," she continued. Adding that all deaths are tragic "whether by bullet or land mine or poisonous gas," she justified acting now by stressing "gas plumes shift and spread without warning; the masses of people they can fell is immense."

"Chemical weapons like other weapons of mass destruction kill on a scope and scale that is entirely different from conventional weapons -- opening the door to them anywhere threatens everywhere."

Rice said only the Syrian army had the capability to unleash an attack of the scale seen in Ghouta. "The opposition does not."

"The intelligence we've gathered reveals senior officials planning the attack and then afterwards plotting to cover up the evidence by destroying the area with shelling," she added. "We assessed he's been using them on a small scale since March" and is "lowering his threshold for use."

Rice said the use of chemical weapons demonstrates a "threat to global security, including the security of the United States."

"Failing to respond to this outrage also threatens our national security," she stressed. "...Failing to respond makes our allies in the region tempting targets."

She also cited "basic human decency" as one of the several reasons listed to respond, along with the proliferation of chemical weapons that could unleash "more fearsome consequences."

"Failing to respond could indicate that the United States is not prepared to use the full range of tools necessary to keep our nation secure. America's ability to rally coalitions and lead internationally could be undermined...it would send a perverse message to those who seek to use the world's worst weapons."