A few days ago, a joint U.S.-U.K-French attack on Syria seemed almost certain. British PM David Cameron stated his intentions of participating in an attack in no uncertain terms.
But because the Labour Party was basically united in opposing an attack, and was joined by many dissident Conservative MPs, the British parliament has snubbed Cameron by voting to stay out of any attack.
The reaction from the Obama regime in America seems to be that they're disappointed by the decision but that it won't stop the attack since the U.S. is capable of carrying out the attacks withour British (or French for that matter) support.
However, Constitutional scholar Barack Obama concluded back in 2007
“the President does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation."
Another constitutional scholar, Joe Biden, agreed with his colleague Barack Obama, and said in 1998 that the constitution says
“the president could not use force without prior [congressional] authorization unless it was necessary to “repel a sudden attack.”
Since the Assad regime clearly does not intend to initiate attacks on the U.S., any U.S. attack on it without congressional approval is clearly unconstitutional according to Obama and Biden.
If U.S. opponents of the war in Congress are really serious about their opposition, it seems clear that they could also stop it, by for example threatening to cut off funding or impeach Obama for doing what he himself in 2007 was unconstitutional.