SENATE SHOWDOWN SET ON DADT, MILITARY FUNDING…. If the Senate follows its schedule today, in about six hours there will be a vote to advance the defense authorization bill. A spokesperson for the Palm Center, a University of California think tank dedicated to repealing the “Don’t Ask, Don’t Tell” policy, said yesterday, “This is the most important vote in the history of the gay civil rights movement.”

That may seem a little hyperbolic, but it’s certainly right up there.

The bill should enjoy broad, bipartisan support. We are, after all, talking about a spending measure that funds the military during two wars. Senate Republicans are, however, going to filibuster the motion to proceed, preventing the chamber from even debating the bill, in large part because of a provision that would empower the administration to end discrimination against gay servicemen and women.

Democrats need 60 votes to overcome Republican obstructionism, led primarily by Sen. John McCain (R-Ariz.). If 60 votes are there, passing the bill with the DADT provision appears very likely. If the 60 votes aren’t there, Republicans will have blocked funding for the U.S. military during two wars, and will have very likely killed DADT repeal for the foreseeable future.

As of this morning, those 60 votes don’t appear to be there. There’s still some time, but the outlook isn’t encouraging.

As mind-numbing as this may seem, “moderate” Republicans may end up killing DADT repeal over a procedural question — how many amendments will be considered to the military spending bill.

On the surface, the dispute Monday centered less on the substance of the bill and more on a procedural question about how many amendments Republicans would be able to offer to the massive defense spending bill.

Two key senators thought to be open to repealing the ban on openly gay soldiers serving in the military — Maine Republicans Susan Collins and Olympia Snowe — complained Monday that Republicans were being shut out of the debate.

Collins “believes that our armed forces should welcome the service of any qualified individual who is willing and capable to serve our country,” said spokesman Kevin Kelley. “She would like the Senate to proceed to a full and open debate on the defense authorization bill, with members able to offer amendments on all relevant issues.”

Just so we’re clear, there’s a very real chance that senators like Collins and Snowe — who claim to oppose the existing “Don’t Ask, Don’t Tell” law — will allow servicemen and women to be thrown out of the military for the indefinite future over a procedural question. The Democratic leadership will allow three amendments; Republicans want more.

Also note, GOP senators like Collins and Scott Brown already supported the spending bill at the committee level. They would, in effect, be filibustering legislation that they’ve already voted for.

For what it’s worth, pro-repeal activists were hard at work yesterday. Organizing for America has made its first foray into gay rights, rallying support for DADT repeal, and the Servicemembers Legal Defense Network hosted a rally yesterday in Maine with entertainer Lady Gaga.

Will the efforts pay off? We’ll know more in about six hours.

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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.