This sounds about right, per the New York Times:
In private, Mr. Obama and his team see the votes as a guidepost for the rest of his presidency well beyond the immediate question of launching missiles at Syrian military targets. If Congress does not support a relatively modest action in response to a chemical attack that killed more than 1,400 people in Syria, Obama advisers said, the president will not be able to count on support for virtually any use of force.
Although Mr. Obama has asserted that he has the authority to order the strike on Syria even if Congress says no, White House aides consider that almost unthinkable. As a practical matter, it would leave him more isolated than ever and seemingly in defiance of the public’s will at home. As a political matter, it would almost surely set off an effort in the House to impeach him, which even if it went nowhere could be distracting and draining.
As a result, Mr. Obama would be even more reluctant to order action in the one case that has most preoccupied military planners: the development of a nuclear bomb by Iran. Any operation to take out Iranian nuclear facilities would require a far more extensive commitment of military force than the missile strike envisioned against Syria. Moreover, a rejection of the Syria strike would make Mr. Obama less likely to leave behind a robust force in Afghanistan after combat troops are withdrawn at the end of 2014.