In another 2 months time it'll be to late.
How's that?
Because primary season will get started and so will Obama's election cycle. It takes a few months for the candidate to be picked, moved through committee, etc. And you have summer recess right before the elections.
The Senators aren't going to want to vote on something that high profile before the election. And if they try to save it until lame duck and the GOP will accuse the Dems on screwing them over and will just delay it until they take over in January.