“This is a very fluid situation,” says a senior Republican Senate aide on the question of filibustering the nomination of Chuck Hagel to be Defense Secretary.  “There are a lot of conversations going on among Republicans about this.”

At this point, Republicans break down into four camps on the Hagel question.  There are at least two senators who actually support the nomination: Nebraska’s Mike Johanns and Mississippi’s Thad Cochran.  There is an unknown number who oppose Hagel’s confirmation but do not support a filibuster that would keep him from receiving an up-or-down vote.  There are those who oppose the nomination and support a filibuster on the merits, or lack of merits, of the nominee.  And finally, there are those — probably just Lindsey Graham, Kelly Ayotte, and John McCain — who oppose the nomination and support a filibuster for other reasons, specifically as a tactic to force the Obama administration to release more information about the deadly September 11, 2012 attack on the U.S. consulate in Benghazi.

It’s not clear exactly how it all breaks down, but the bottom line is there will be a cloture vote on the Hagel nomination, and a lot of Republicans will vote to prevent it from going forward.  It takes 60 votes to overcome a filibuster, and all 55 Senate Democrats are thought to support Hagel.  Of the 45 GOP lawmakers in the Senate, start by taking away Johanns and Cochran.  That leaves 43.  If there any other supporters, or if the group that opposes a filibuster on principle has three or more senators in it, then Republicans won’t be able to muster the 41 votes they need to uphold the filibuster, and it will fail.

Democrats have sometimes accused Republicans of engaging in an unprecedented effort to block Hagel.  That’s true only if one confines the conversation to Secretaries of Defense.  And even in that category, while there has never been a filibuster against a Pentagon nominee, there has been one famous episode — John Tower in the George H.W. Bush administration — who was rejected by the Senate in an up-or-down vote.

But there have been cabinet-level filibusters in the last decade.  Senate Republicans point out that there was a cloture vote on John Bolton, who was stopped as a nominee for UN Ambassador in 2005; there was a cloture vote on the nomination of Dirk Kempthorne to be Secretary of Interior in 2006; and there was a cloture vote on the nomination of Stephen L. Johnson to be head of the EPA in 2005.

Now, Hagel presents a difficult situation for Republicans.  A large number of them believe he is simply unqualified to run the Pentagon.  But they respect the principle that a president should be able to get the cabinet appointments he wants.  According to Senate sources, it is a newcomer, freshman Sen. Ted Cruz, who is arguing most forcefully that that principle should not apply in this case, at least not right now.

“Cruz has been making very compelling arguments publicly and privately as to why Hagel is an extraordinary case and that a final vote should be delay until Hagel is more forthcoming about past speeches and finances,” says the Senate aide.  “Assuming these things are provided over the next couple of weeks, it will be up to the senators who oppose cloture tomorrow to decide whether this perfectly reasonable requirement has been met.”