Update (4:59 p.m.): The cloture vote fails, 58-40-1, to move Hagel's confirmation forward and end the filibuster. A new vote will be set for after Senate recess, likely either on February 25 or 26. (Here's for our full updated report.)

Update (4:46 p.m.): As a cloture vote presses on, it appears that Reid may come up short at between 57 and 59 votes, which would likely force Reid to reschedule for a week and a half from now. It's possible that a Senator may switch a vote, however, pushing Hagel toward confirmation with 60 votes.

Update (3:30 p.m.): Reid has scheduled the cloture vote for 4:15 p.m. It still needs 60 votes to move to confirmation. If it fails, that might set up a vote for the week of February 25.

Update (2:00 p.m.):  The White House sent a letter to Sens. John McCain and Linsdey Graham today admitting that President Obama did not personally call the Libyan leaders on the night of the Benghazi attack. That is one of the issue that Senator Lindsey Graham and others have been hammering the President on and demanding a response. With that be enough to appease them and head off a filibuster? The two sides are reportedly working on a "compromise" that would delay the Hagel vote until after next week's recess, but allow him to go forward without a cloture needing to be taken. CNN's Dana Bash has been staying on top of the deatails.

white house is now in full court press mode re hagel. biden is burning up the phone lines. im told he called murskowski too

— Dana Bash (@DanaBashCNN) February 14, 2013

Original post: Senate Majority Leader Harry Reid has scheduled a vote tomorrow (Update: today at 4:15 p.m.) to decide the fate of Defense Secretary Nominee Chuck Hagel, setting up a game of chicken with Republicans who are threatening to block him. Friday's vote will not be a vote to confirm Hagel, of course. First, we have to get through cloture, which as we all know by now requires 60 votes to end debate, allowing for actual vote on his confirmation to take place. Reid will need five Republican Senators to vote with his 53 Democrats (and two Independents) for cloture motion to pass and word out of Washington at the moment is that he doesn't have them.

The key will be, as usual, John McCain. The Senator from Arizona is still not happy about the answers he's been given on the Benghazi debacle and even though Hagel is a former Republican who had nothing to do with Libya, McCain senses the opportunity for leverage over the White House. If he gives in and allows cloture—and the up-or-down vote on Hagel—then others will likely follow, but it's still not fully clear just how far he's willing to push it. Reid says he's been told the filibuster is happening.

Susan Collins of Maine is one Senator who is on the record as saying she will vote against Hagel's nomination, but will vote for cloture so that he gets his shot on the floor. But Collins won't be bringing anyone else with her. Georgia's Johnny Isakson basically said he's waiting for McCain's go-ahead, announcing that he wouldn't make a decision "Until I hear from John McCain." While he's waiting, the current Secretary of Defense is technically walking off the job today (though he won't actually leave the Pentagon without a boss.)

Successfully filibustering a cabinet nominee (which is what cloture would prevent) has never been done before and even McCain recognizes that it would be a bad precedent to do it just to score an unrelated political win. (There are other options as well, such as voting for cloture, then immediately putting the Senate in recess creating an indefinite delay.) Not seeing another option on Benghazi, however, McCain may take the gamble and hope the White House blinks.

So the next 24 hours is looking like a standoff, with Republicans betting that the President will just tell them what they want to know, and Democrats hoping that Republicans will look like madmen who can't be reasoned with. A few are probably even hoping they do get a filibuster just to make the GOP look ridiculous. That's the best reason of all for Reid to go through with Friday's cloture vote, though maybe he wishes he'd saved himself the headache and shoved through filibuster reform when he had the chance.