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One informed Congressional observer tells Business Insider that the support will be there in the Senate but the House looks very iffy:
Senate should be ok to pass. But the House vote seems very difficult. Think about all of those House GOP members that want to avoid tough votes on the [continuing resolution], debt ceiling, farm bill, and immigration. They were trying to avoid these votes for their primaries and don't seem convinced an attack would be particularly useful. Now they have an even tougher vote in front of them coupled with the anti-war Dems. This is TARP on steroids. And remember how the Iraq votes realigned
Basically, if you're a member of the House, in either party, it's a lot easier to come up with good political reasons to vote "no" on attacking Syria than "yes."
Democrats: In the current political environment, they have little reason to think voting against an attack will make them look "soft on terror," which is what they were most afraid of during the Iraq authorization vote 10 years ago. But they have good reason to fear the Hillary example: voting yes could cost them a primary election if things go wrong.
Republicans: War hawks are a far weaker force in GOP politics than they were 10 years ago. You don't have to be Ron Paul to defend a skeptical position on intervention anymore. And it's not that hard to make a case to a Republican primary electorate for why you opposed one of Barack Obama's initiatives.
That said, a very large share of members of the House are probably genuinely undecided right now on how to vote. The same observer noted that most public statements from members of Congress so far have been pointedly non-committal. Members have focused their comments on the importance of consulting with Congress or seeking a congressional vote; they have avoided commenting on where they actually stand on an attack itself.
Sen. Marco Rubio's (R-Fla.) statement is a perfect example: somehow, he finds a way to spend several hundred words lambasting the President's handling of the Syrian situation without actually taking a position on what should be done. Does Rubio even know how Rubio will vote?
If he and many other members have really not made up their minds yet, then the president has a shot to get authorization for his attack. But he's going to have to overcome unfavorable political terrain to do it.