As with DREAM, passing it would mean at least two Republicans broke their pledge not to vote yes on anything until the tax cuts bill is enacted. The key difference here: They’re close to 60 votes for repeal and they’ve gotten plenty of political cover from Gates, Mullen, and that Pentagon study to pull the trigger. A Republican House won’t sign off on it next year so Senate fencesitters are keenly aware that this is their last chance. And as Gates has been reminding them, if they don’t act now and do this in an orderly democratic fashion, the courts are apt to intervene anyway and strike down DADT sooner rather than later. Pressure.

As of this writing, there are at least three Republicans willing to repeal — Brown and Collins said yes last week and Murkowski joined them this afternoon — but they’re demanding a bit more procedural leeway from Reid as a price for their votes. If he refuses and calls their bluff by forcing a vote, will they hold the line or cave? Greg Sargent on the wrangling between Reid and Collins:

Collins has said she supports repeal, but won’t agree to vote for cloture on the Defense Authorization Bill containing repeal if Harry Reid doesn’t allow ample time for open debate and amendments on the bill…

[T]he aide close to the talks defended Reid’s decision [to bring the bill to the floor tonight], arguing that it’s just as risky to postpone the vote on repeal. “There’s concern that members of her caucus will be out the door as soon as we pass everything Republicans want,” the aide says…

A spokesman for Collins flatly denies she asked Reid for unlimited debate. Rather, the spokesman says, Collins has pointed out to Reid that the average number of days spent debating previous defense authorization bills has been 11 days, with an average of 14 or so amendments considered. Collins has asked Reid to come up with a comparable offer, the spokesman says.

No one appears to be disputing that the talks have hit a snag, though.

Murkowski is also demanding an “an open and fair amendment process.” Reid can’t open it up too much, though, as allowing unlimited debate would let DeMint, Coburn, McCain or some other repeal opponent slow things down and obstruct the vote. Reportedly, he offered Collins 15 amendments, 10 of which would come from the GOP, and she turned him down. Which is where the suspense comes in: Will she and Murkowski agree to some limits on debate? And if not and Reid pushes the bill tonight, will either they or Scott Brown relent and vote yes anyway? I’d say Murky’s a fair bet to cave since she won’t face another election for six years, and if the Dems hold together and get to 59 with her, Scotty B will be hard-pressed to vote no and be the man who singlehandedly killed the DADT repeal when he’s facing Massachusetts voters next year.

If they do vote today and fall short, that’s not necessarily the end of the process. Reid and Collins could agree to some procedural patch enabling another vote before the lame duck ends. Tonight’s vote will be interesting anyway, though, just to see how close they get. Exit question: If Liz Cheney is for it, who can be against it?

Update: Looks like they couldn’t reach a deal with Collins to proceed this evening. Are Brown and Murky still in play?