What message would that send? No worse than the one the administration has already sent by the Russian roulette fiasco. Said the Journal: “What could be worse for America's standing in the world than a Congress refusing to support a president's proposal for military action against a rogue regime that used WMD? Here's one idea: A U.S. president letting that rogue be rescued from military punishment by the country that has protected the rogue all along.”
In fairness to Obama, presidents shoulder an enormous burden. They will always be blamed for doing too little or doing too much. Just ask George W. Bush, whose bold and constant stances drew so much scorn from Obama and Secretary of State John Kerry.
If Syria gets a pass on the gassing and another more horrendous episode occurs, Obama can say he tried to prevent it but Congress wouldn't let him. But the administration's own incompetence and inconstancy will play a role that this president will likely never acknowledge.