This is not, as I understand it from ABC’s timetable, the key vote that Cruz and Lee want filibustered. This is the vote to end debate on the motion to proceed; after 30 hours, they’ll have another vote on the motion itself, at which point Reid will file his amendment stripping the defunding language out of the House bill. Then, on Saturday, comes the key vote — a cloture vote to end debate on Reid’s amendment. Reid needs 60 for that, and if he gets it, he can pass his amendment with a simple majority on Sunday.

So why are we interested in this vote? Because, after Cruz’s ironman efforts in support of a filibuster, it might give us a sense of whether the “defund” caucus has grown overnight. (Jeff Sessions, formerly a skeptic of the Cruz/Lee strategy, announced last night that he’d vote with them. At some point, the politics of this will tilt Republican fencesitters towards siding with Cruz so long as they know their individual votes won’t actually get him to the 41 he needs.) No guarantee, though: Cruz himself might vote for cloture today just to move things along and get to the big showdown on Saturday. But maybe the defunders are planning to treat each of the upcoming votes as a test of strength, voting no at each step to signal their opposition even though they know they’re going to be outvoted. Turn on C-SPAN 2 and we’ll see what happens.

Key question now for McConnell and Boehner: Is there any way to speed this up? If they stick to the schedule, the House won’t get Reid’s clean CR back until Sunday night, with a shutdown set to happen on Monday. (Reid himself alluded to this after Cruz finally ended his speech, snidely dismissing it as having been a waste of time.) There’s chatter among Senate Republicans about yielding back some of their floor time during the coming days, but maybe that would look extra RINO-y after Cruz’s marathon floor session. Meanwhile, in the House, Boehner’s reportedly considering adding a one-year delay for the individual mandate once he gets Reid’s bill and sending it back to the Senate. If he does that, it means a shutdown since Senate Dems will block it. But a temporary delay on the individual mandate after Obama already unilaterally delayed the employer mandate is better politics for the GOP during a shutdown than a straight defunding effort is.

Stand by for updates.

Update: A new report of tension in the caucus room:

Boozman, an Arkansas Republican elected in 2010, stood up and yelled at Cruz, expressing frustration that his staff was deluged with belligerent phone calls mostly from out-of-state activists attacking the senator over the issue of defunding Obamacare, according to several sources familiar with the exchange. Boozman also slammed Cruz for suggesting Republicans were in favor of the three-year-old law even though all of them opposed it and have repeatedly voted to repeal it.

Staring at Cruz, Boozman said he hasn’t been bullied since the seventh grade and he wouldn’t be bullied now.

Several Republicans cheered Boozman and one quipped: “A sleeping bear had been awoken.”

Boozman naturally declined comment when asked about it by reporters. NBC claimed last night that Rand Paul had sided with McConnell in the same meeting by arguing against Cruz’s filibuster strategy. That’s not improbable — Paul has been sour on the prospects of a shutdown and was pushing his own alternative to the defunding strategy even before Cruz began his speech yesterday afternoon — but he did end up coming to the floor last night to show support for Cruz once the speech had begun. If tea partiers are your base, there’s no way to be safely on the other side of this issue from Cruz right now. At least publicly.

Update: Nope, not a test vote. All 100 senators voted to end debate on the motion to proceed. Maybe tomorrow’s vote, on the motion itself, will be the test.