The US Congress is holding its first public hearing about plans for military intervention in Syria as Barack Obama tries to convince the country of the need to respond to the chemical weapons attack.
Secretary of State John Kerry, Defence Secretary Chuck Hagel and Joint Chiefs chairman General Martin Dempsey were to appear before the Senate Foreign Relations Committee . A classified briefing open to all members of Congress was planned as well.
Mr Obama surprised the world over the weekend when he announced he would seek congressional authorisation for limited military strikes against Bashar Assad's regime.
The US says it has proof that the Assad regime is behind attacks that Washington claims killed at least 1,429 people, including more than 400 children.
Now Mr Obama is sending his top national security advisers to the Capitol for briefings. And he is meeting leaders of the House and Senate armed services committees, the foreign relations committees and the intelligence committees.
He has already won conditional support Monday from two of his fiercest foreign policy critics, Republican senators John McCain and Lindsey Graham.
They said they would be more willing to support Mr Obama if the US sought to destroy the Assad government's launching capabilities and committed to give more support to the rebels.
Mr McCain said he is prepared to vote for the authorisation but he would not support a resolution that fails to change the situation on the battlefield, where Assad still has the upper hand.
Robert Menendez, chairman of the Senate Foreign Relations Committee, said he believes the panel will back Mr Obama if the administration explains "the full case" for the use of force and what it sees as the end result. "Not acting has huge consequences," he said.
After a decade of war in Iraq and Afghanistan, polls show most Americans opposed to any new military action overseas.
Some say Mr Obama still has not presented good enough evidence that Assad's forces were responsible for the chemical attack. Others say the president has not explained why intervening is in America's interest.
Those questions come a decade after the Bush administration badly misrepresented the case that Iraq's Saddam Hussein possessed weapons of mass destruction.
The Obama administration argues that the United States must exert global leadership in retaliating for what apparently was the deadliest use of chemical weapons anywhere over the past 25 years.
The administration argues that the sarin gas attack last month violated not only the international standard against using such weapons but also Mr Obama's "red line," set more than a year ago, that such WMD use would not be tolerated.
Syria's conflict has claimed more than 100,000 lives. The fight has evolved from a government crackdown on a largely peaceful protest movement into a full-scale civil war reminiscent of the one that ravaged Iraq over the last decade. Ethnic massacres have been committed by both sides, which each employ terrorist organisations as allies.