The reason that U.S. President Barack Obama passed the buck on authorizing a military strike on Syria to Congress is not because getting congressional approval is the constitutional thing to do. It always has been, although presidents have regularly denied it. Rather, Obama passed the buck to Congress because it was the only way out of the dilemma that he imposed on himself when he declared the use of chemical weapons to be a red line, without having thought through whether or how to go to war if the line was crossed.

Read here – Foreign Affairs