Obama on Saturday unexpectedly stepped back from ordering a military strike under his own authority and announced he would seek congressional approval.
On Wednesday, Kerry, Defense Secretary Chuck Hagel and the chairman of the Joint Chiefs of Staff, Gen. Martin Dempsey, were trying to make their case in a public hearing before the House Foreign Affairs Committee.
They and other senior administration officials also were providing classified briefings to the Senate Foreign Relations and Armed Services committees.
But even supporters of military action urged Obama to do more to sell his plans to an American public that is highly skeptical after a decade of war in Iraq and Afghanistan.
Obama is expected to find little international support for action. Among major allies, only France has offered publicly to join the United States in a strike.
The United Nations secretary-general has warned that any “punitive” strike on Syria would be illegal without a sound case for self-defense or the approval of the Security Council, where Syria ally Russia has used its veto power to block action against Assad's regime.
