As I noted below, it’s becoming clearer and clearer that Dems may not be able to muster a simple majority in support for Obama’s jobs bill in the Senate later today.

That’s because of likely uniform GOP opposition, yes, but also because some Senate Dems in red states appear to be prepared to vote against the jobs bill — even though what’s being voted on today is merely over whether it will go to the floor for debate.

And then there’s yet another category: Senate Dems who support the jobs bill but may not show up to vote today.

Jeanne Shaheen, the Dem Senator from New Hampshire, is scheduled to be in Boston tonight to accept the “New Englander of the Year” award, according to her Senate Web site. Needless to say, that coincides with tonight’s Senate vote on the American Jobs Act.

So will she be voting on the bill?

Jonathan Lipman, a spokesperson for Shaheen, tells me that she supports the bill, but that she’ll only be on hand to vote for it if her vote is necessary. “The Senator has told leadership that she is fully prepared to be here tonight if her vote is needed for passage,” Lipman says.

By “passage,” however, Lipman appears to mean getting the 60 votes for cloture. No one expects that to happen. The emerging question right now is whether it will gain a simple majority in the Senate. That’s crucial for Dems, because if it doesn’t, it will give the GOP a talking point to undercut the Obama/Dem case against the GOP. Republicans will argue that not even a majority of the Dem-controlled U.S. Senate supports the bill, so why are they being singled out by Obama for frustrating the will of the majority on jobs? And if a majority doesn’t back the bill, it will be widely portrayed in the media as a major rebuke to the President.

Thus far, it doesn’t look like Shaheen will be on hand (though that could change). But to get that simple majority, Dems need every vote they can get — and right now, it’s looking very, very dicey. More when I learn it.

UPDATE: Emily Heisig, a spokesperson for the New England Council, which has endorsed some of Obama’s job creation ideas (but not the whole jobs bill), emails:

We would be disappointed, but we would understand if there’s an important vote and the Senator needs to be there for it. Part of the reason we’re honoring her is she’s been a good advocate for this region.

UPDATE II: It’s official: Senator Shaheen will in fact return to the Capitol and vote for the jobs bill. Her spokesman Jonathan Lipman emails:

The Senator will be returning to the capitol tonight and leadership intends to hold the vote open for her. She will be able to vote.