The Obama campaign would like nothing more than to pass the magic number tonight and declare victory. They know that if they can credibly claim 2,118 delegates this evening (or tomorrow), the force generated by the media coverage of the event will be overwhelming and will help shut down the race. Once that genie is out of the bottle, so to speak, it can never be put back in, and it will make it that much harder for Clinton to mount an effective challenge at the convention - should she choose to do so.

Obama is currently 42 delegates short in the RCP count (and a bit less in the Obama campaign's own count). Between Montana and South Dakota there are 31 delegates up for grabs tonight, and according to estimates if Obama wins 55-45 this evening the delegate split will be in the 17-14 range, plus or minus.

That means Obama will need about 25 supers to declare for him today in order to claim victory tonight. (And remember, supers from MI and Fl only count for half a vote). That seems like a fairly tall order - though certainly possible - and as Adam Nagourney reports today, the Obama campaign has been trying to organize a show of force to try and put him over the top:

Obama campaign advisers said that they were orchestrating an endorsement of Mr. Obama by at least eight Senate and House members who had pledged to remain uncommitted until the primaries ended, and that the endorsements would come the moment the South Dakota polls closed on Tuesday night.

We'll have a better idea about Obama's chances of going over the top tonight as we see the flow of declarations from superdelegates, but it seems like it's going to be very, very close.

UPDATE: For the record, two supers have declared for Obama this morning: Missouri State Rep. Maria Chappelle-Nadal, and Michigan superdelegate Joyce Lalonde.

UPDATE II: The Chicago Tribune quotes an anonymous source saying Obama will get across the finish line tonight:

A Democratic source said at least five to 10 House members would endorse Obama on Tuesday morning, at least 10 senators will endorse him by the end of the day and an additional 10 superdelegates will also endorse him during the day. That would assure enough delegates by the end of the day to clinch the nomination. The source declined to be identified because he was not authorized to disclose the information. Obama was about 40 delegates away from the nomination on Monday.