SHOWDOWN OVER STATE, TEACHER AID DELAYED…. It was poised to be a pivotal moment in the Senate, and a key test of the chamber’s Republican “moderates.”

Democrats had crafted a package with $10 billion to save school teachers’ jobs, and $16.1 billion in state Medicaid funding (FMAP). The measure was financed through a combination of cuts and closing foreign tax credit loopholes. For Republicans who claim to want to improve the economy, but not at the expense of the deficit, there were no excuses — Dems offered a modest, sensible bill, which would save jobs, help struggling states, all without adding to the deficit.

But before the GOP “moderates” could come up with some new rationalization to once again block a jobs bill, the package ran into some CBO trouble.

The Senate tabled a jobs measure Monday because Democrats underestimated the package’s cost.

Democrats had scheduled a vote to end debate on their proposal … but the Congressional Budget Office (CBO) scored the bill and found that it wasn’t fully paid for, Senate Majority Leader Harry Reid (D-Nev.) said Monday.

“Certain spending cuts did not save the [money] that we needed,” Reid said.

Senate Democrats’ proposal included budget numbers that were part of a CBO score of a previous House measure, but those costs had since changed, Reid said.

As structured, the bill would be partially paid for, the CBO concluded, but would nevertheless add $5 billion to the deficit.

Ideally, this wouldn’t much matter. When Republicans don’t like CBO scores, they ignore them and say the CBO doesn’t matter anyway. What’s more, it’s $5 billion. If it were tax cuts or Pentagon spending, $5 billion would be considered a rounding error.

But when it’s teachers’ jobs on the line, a bill that’s only mostly paid for, and which enjoys the support of a majority of the Senate, can’t even get a vote.

The Senate leadership will scramble today to address the shortfall and ensure that the bill is paid for, which in turn will set up another showdown — and other opportunity for Senate Republicans to undermine the economy. The GOP will also continue to make the process as long as possible — this is the last week before the chamber’s August recess — in the hopes that absolutely nothing can get done before senators head home.

In the meantime, even if the Senate somehow manages to find one GOP vote and pass this bill, it will head back to the House, which is already in recess and won’t return until September. In the interim, teachers will lose their jobs, and get a lesson in how Republican officials are slowly chipping away at the ability of our institutions to function.

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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.