? When senators delaying a vote say it isn't, according to Senate Republicans who are blocking President Obama's nomination of Chuck Hagel to be defense secretary.
When is it a filibuster then? When a senator either drones on and on as in the old days or, increasingly, just threatens to.
Those seem to be the wacky ground rules as senators battle over their former colleague's nomination.
Right now, they're taking a short intermission after Republicans blocked, at least temporarily, a vote on Hagel's nomination on Thursday.
Another vote is scheduled for Feb. 26 when the Senate returns from its 10-day break.
Democrats control 55 votes in the 100-seat chamber and easily have more than the 51 votes needed to confirm the former Republican senator from Nebraska.
But Senate math is more complicated.
By rules and tradition, 60 votes are required to break a filibuster or other delaying tactics just to get to that up-and-down vote.
Right now, Democrats don't have them. They only mustered 58 on Thursday in their let's-get-on-with-it vote.
"This is not a filibuster," Sen. James Inhofe, R-Okla, said to colleagues. "We just want to have a 60-vote margin."
Both sides believe Hagel will eventually be confirmed. That's why Republicans insist they're not filibustering, just bidding for more time to seek fresh material on the nominee.
"We need more information and we have a right to get it," said Sen. Lindsey Graham, R-S.C.
Senate Majority Leader Harry Reid, D-Nev., and Obama are crying foul.
"There's nothing in the Constitution that says somebody should get 60 votes," Obama said. "It's just unfortunate that this kind of politics intrudes at a time when I'm still presiding over a war in Afghanistan and I need a secretary of defense."
Obama was wrapping up three days of travel to promote his State of the Union proposals on Friday in Chicago, then heading to Palm Beach, Fla., for the long holiday weekend.
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