In about 45 minutes or so, the Senate will vote on its stopgap spending bill that would keep the government’s lights on until November. It’s very similar to the bill approved by House Republicans, except for one thing: it treats emergency disaster funding as an emergency — without offsets — the way Congress has always rallied to provide aid for communities in need.

As far as the Senate Democratic leadership is concerned, this afternoon — and indeed, the whole process — should be pretty straightforward. The clean spending bill will come to the floor, based on the budget framework both parties agreed to in early August. It will pass, then go back to the House for its approval. Once the lower chamber passes it, President Obama will sign it and the shutdown will be averted.

But the plan probably won’t unfold this way.

The problem, at least one of them, is the GOP filibuster. Two weeks ago, when the Senate took up FEMA funding without offsets, it passed easily with a bipartisan majority. It was a 62-37 vote, with nine Republicans joining the Democratic majority. If those same GOP senators follow through and vote the same way today, the Senate’s spending measure should pass with relative ease.

But the odds now seem against it. The measure will get some GOP votes, but Senate sources tell me the likelihood of getting enough votes to overcome Republican obstructionism is poor. For the GOP senators who did the right thing two weeks ago, it’s now better to side with House Republicans than communities in need of disaster aid.

Keep in mind, the only point of contention here is over disaster relief — Republicans are holding it hostage, and Democrats don’t want to pay the ransom. The GOP list of demands is fairly brief — the right is demanding cuts from clean-energy programs to offset some of the costs to finance FEMA — but Dems aren’t the only ones opposed to the Republican requirements. In fact, just last week, both the U.S. Chamber of Commerce and the U.S. Conference of Mayors said the GOP approach would cost jobs.

At this point, congressional Republicans, in both chambers, don’t seem to care. Imagine that.

When the vote is held around 5:30 eastern, either the GOP filibuster will kill the bill or it won’t. If the filibuster fails, the clean bill will go back to the House, which will have to act sometime this week. And what if the filibuster succeeds? No one seems to know what will happen, because at that point, Democrats won’t want to pass the pathetic House scheme, and Republicans won’t let the Senate vote on the more responsible Dem version.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.