The headlines notwithstanding, I don't see it as a gamble; rather I see it as a stroke of genuius, his only way out of a losing hand that probably will be lost: Obama Presses Syria Gamble - Reversing Course, White House Races to Get Congressional Backing for Strikes

From The Wall Street Journal:

The White House raced on Monday to persuade Congress to authorize military action in Syria, after President Barack Obama, in one of the biggest gambles of his presidency, handed the volatile issue to lawmakers who have given him few recent legislative victories.

The president's surprise reversal put on hold a military mobilization that had appeared on the verge of launching missiles and sparked urgent lobbying for a Congressional resolution authorizing force. The president must win over those Republicans calling for a broad U.S. mission against Syria, as well as lawmakers in both parties who are wary of even limited strikes.