It's called the law of the jungle. If the US can bend enough arms it will
do it with the fig leaf of the UN. If not, it will do it anyway if it
doesn't fear the consequences.
The chemical arms claim is completely bogus. It has been reported that the
"rebels" were the ones using the chemical arms and conclusively confirmed
when some of them were arrested in Turkey with chemical weapons.
America's Democratic/Republican duopoly is frantic that their "rebels",
elsewhere labeled as terrorists by the same people, have not only lost
political support from the average Syrian (yes, religious-inspired
beheadings, summary executions, kidnappings, random murders, and extreme
Islamic religious courts do have consequences) but are also losing
disastrously militarily.