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.
When the red line was crossed, the administration's belated search for military options faced two contradictions. The first was between the strong incentives to retaliate against the government of Bashar al-Assad and the wide opposition in both the United States and outside world to U.S. military action. The second was between the amount of force that would have a chance of producing useful strategic results and the amount that is politically tolerable. Even among those who demand action, pressure to use U.S. military power is exceeded by pressure not to use very much of it, for fear of entanglement that clearly does mean war.