Whatever Senate Republicans are calling it, what's happening to Secretary of Defense nominee Chuck Hagel right now is a filibuster. (J. Scott Applewhite -- AP)

Thursday night, a vote was called to invoke cloture on Chuck Hagel's nomination to become secretary of defense, and thus move to a final confirmation vote. The cloture vote failed. Only 58 senators voted yes, short of the 60-vote cloture threshold, with Sens. Thad Cochran (R-Miss.), Susan Collins (R-Maine), Mike Johanns (R-Neb.), and Lisa Murkowski (R-Alaska) joining a unified Democratic caucus in voting yes. The rest of Hagel's former Republican Senate colleagues voted against him. Given that Senate Majority Leader Harry Reid (D-Nev.) voted no for procedural reasons (it allows him to bring another cloture vote in the future), that puts Hagel only one vote short of breaking a filibuster.

Except Republicans don't want to call it that. "It's not a filibuster. I don't want to use that word," Sen. James Inhofe (R-Okla.) told Foreign Policy's Josh Rogin. Immediately after the vote, Sen. John Cornyn (R-Tex.) agreed, taking to the Senate floor to declare, “This is not a filibuster." Sen. Lamar Alexander (R-Tenn.) issued a statement clarifying that while he "believe[s] a president’s cabinet members deserve an up-or-down vote," he also thinks "the majority leader’s motion to cut off debate only two days after an important nomination is reported to the Senate floor is premature."

It is rather hard to come up with a plausible definition of "filibuster" that excludes what Senate Republicans did Thursday. My colleague Rachel Weiner wrote an excellent piece on this very question Thursday, and found that most serious experts agree that invoking cloture to prevent Hagel's nomination from coming to a final vote is absolutely a filibuster.

Gregory Koger, a University of Miami political scientist whose book "Filibustering" is quickly becoming the canonical work on the subject, tells Weiner that the Hagel action qualifies under his working definition of "filibuster," which is, "legislative behavior (or the threat of such behavior) intended to delay a collective action for strategic gain." In his book, he writes that "a typical 'filibuster' occurs when a senator refuses to agree to a time to hold a vote on a measure and, implicitly, threatens to drag out the debate indefinitely." If Alexander isn't being disingenuous, he could protest that he is explicitly not threatening to drag out the debate "indefinitely." But even if the Hagel filibuster does not count as a "typical" filibuster — and it's too early to tell if Republicans really do intend to drag this out indefinitely, so it may be a typical one yet — it's still absolutely a filibuster.

Sarah Binder, a political scientist at George Washington University who specializes in Congressional, and in particular Senate, procedure, agrees. "Let’s put to rest the debate about whether insisting on sixty votes to cut off debate on a nomination is a filibuster or, at a minimum, a threatened filibuster," she writes. "It is." Just because the minority has succeeding in requiring 60 votes to do anything in the Senate doesn't mean they're not filibustering everything. Quite the opposite — everything, in effect, is now subject to a filibuster by being subject to a 60-vote threshold, as Jon Bernstein explains here.

Deputy Defense Secretary Ashton Carter, who will serve as acting secretary should Leon Panetta leave before Hagel is confirmed. (Evy Mages -- For The Washington Post)

And just looking at cloture votes doesn't give a full picture, Binder says. Republicans wouldn't let the nomination of Health and Human Services Secretary Kathleen Sebelius and former Commerce Secretary John Bryson go forward without Reid first agreeing to use a 60-vote threshold for each. They didn't face cloture votes, but they were filibustered all the same.

In any case, the use of the filibuster to try to block a nominee from even getting confirmed is largely unprecedented. Binder notes that cloture was invoked on Commerce Secretary William Verity in 1987 and Interior Secretary Dick Kempthorne in 2006, but that was to end holds placed by certain senators using the nominations as leverage on other issues. Ted Kennedy considered filibustering Attorney General John Ashcroft in 2001, but Judiciary Committee Chairman Patrick Leahy and minority leader Tom Daschle opposed a filibuster, and one was not forthcoming. That would have been the clearest precedent for what's happening to Hagel now, but it didn't happen.

So what happens now? If Defense Secretary Leon Panetta resigns in the next few days, as expected, then Deputy Secretary Ashton Carter will assume the post of Acting Secretary. That has happened twice before. Bill Clements, who would later become governor of Texas, served for 39 days as Acting Secretary in between Secretaries Elliott Richardson (who left to become Attorney General) and James Schlesinger in 1973. William Howard Taft IV (the great-grandson of the president) served for 59 days at the start of George H.W. Bush's presidency, in between the failure of the initial nominee for secretary, John Tower, and the confirmation of his replacement, Dick Cheney.

And Carter, by all accounts, is more than qualified. He has served as either undersecretary for acquisitions, technology, and logistics (the post that manages defense purchases and the day-to-day running of the department) or deputy secretary since Obama took office. He was widely rumored to be among those considered to succeed Panetta, and is in the running to replace Steven Chu as Energy Secretary.

Other departments have survived long stints with acting directors. Jeffrey Zients has been acting director of OMB since January 2012, and combined with a previous stint, has served a total of 496 days — longer than his predecessor Jack Lew's time as Obama's budget director, and almost as long as Peter Orszag, who served 556 days. Acting Secretary of Commerce Rebecca Blank has served 330 days, longer than Secretary John Bryson, and continues in the role as America's Commerce Cabinet Crisis continues.

So the Defense Department will survive if Hagel's confirmation is delayed. But make no mistake. Republicans are filibustering Hagel, and no Cabinet nominee has been truly filibustered before.