I think it is prudent to go back to June 2011 and remind everyone that President Obama took us to war in Libya without congress.   He even stayed in the conflict after his own Office Of Legal Counsel advised him he was violating constitutional law:

(June 2011 – New York Times)  President Obama rejected the views of top lawyers at the Pentagon and the Justice Department when he decided that he had the legal authority to continue American military participation in the air war in Libya without Congressional authorization, according to officials familiar with internal administration deliberations.  (link)

(Via Politico)  Secretary of State John Kerry on Sunday said if the Assad regime in Syria “were to be foolish enough to attack yet again and to do something in the meantime,” President Barack Obama “knows he has the power” to attack unilaterally and would likely “move very, very rapidly” — but “he feels we are stronger” moving with congressional authorization.

Host Chris Wallace asked Kerry on “Fox News Sunday” what message the U.S. is sending to “Iran and Hezbollah and North Korea when the president announces he thinks we should take military action, but he’s going to wait nine days for Congress to come back before he takes any action, and then he goes off and plays a round of golf?”
“I think actually North Korea and Iran ought to take note that the United States of America has the confidence in its democratic process to be able to ask all of the American people to join in an action that could have profound implications with respect to Iran,” Kerry said. “The fact is that if we act, and if we act in concert, then Iran will know that this nation is capable of speaking with one voice on something like this, and that has serious, profound implications, I think, with respect to the potential of a confrontation over their nuclear program. That is one of the things that is at stake here. “  (continue reading)