Few public policy choices are easy, with almost all the arguments on only one side of the ledger. Most issues are nested in complex contexts, with conflicting priorities and multiple goals at stake. Even if the decision is narrowly balanced, a 51-49 choice, it has to be defended 100%. That's the problem the administration has now with Syria -- and the problem faced by the members of Congress who will have to vote yea or nay.
There are strong arguments for supporting punitive strikes on Syria and strong arguments against. Now that the President has made his decision, his team is pulling out all the stops to win the fight in Congress -- secret briefings, a nationally televised speech, a lobbying alliance with AIPAC, and more to come. I wouldn't be surprised if someone launches a "are you with President Obama or President Putin?" campaign.
The opposition is fragmented -- Democrats who are anti-war; Republicans who are viscerally anti-Obama, no matter the issue; politicians who want to follow local public opinion, which so far has been pretty negative on air strikes. They know what they don't want but have no common vision of an alternative policy.
So be prepared for strident, black-or-white arguments in the days ahead. Despite the news articles giving overwhelmingly negative vote counts, my guess is that the Senate will approve the bipartisan measure from the Foreign Relations Committee and that that will give the administration momentum in the House that will lead to a very close vote, too close to call right now.
PS: I've been wrong on these calls before but try to forget when.