Democratic senators will endorse Obama

Obama supporters have been "pressing" for these superdelegates to endorse early this week, but according to one source, "the senators don't want to pound Hillary Clinton, and there is a sense she should be given a grace period."

A series of meetings on the topic have been facilitated at different times by Illinois Sen. Dick Durbin, former Senate Minority Leader Tom Daschle and Iowa Sen. Tom Harkin. Durbin and Daschle are Obama supporters, while Harkin is uncommitted.

Obama is now 46 delegates short of the 2,118 needed to clinch the Democratic nomination, while Clinton needs 202. There are 31 pledged delegates up for grabs in the Tuesday contests, and 202 superdelegates have yet to commit to either candidate.

I think it's only now that we're finishing these contests that people are going to actually reflect," Clinton said on her campaign plane Sunday, referring to the uncommitted superdelegates. "Who's our stronger candidate? And I believe I am, and I'm going to make that case, and at some point it will either be accepted or it won't be, but I feel strongly about making it."

Clinton argued that even superdelegates who have committed to Obama are free to "change their minds" -- a suggestion the Obama campaign declined to comment on.

Despite the odds against her, Clinton continues to pick up support even as Obama grows his lead among superdelegates.