The specter of the bogus claims that former Iraqi dictator Saddam Hussein was hiding weapons of mass destruction — used to justify war —  hangs over the debate on how world leaders will respond to the possibility that Syria deployed chemical weapons.

Obama administration officials say they know they have to deal with the Iraq WMD legacy and will need definitive proof to persuade Russia, Syria’s only remaining ally in the U.N. Security Council, that Bashir Assad’s regime used deadly sarin gas against the opposition in the country’s bloody two-year civil war.