After the Republicans raised the potential for a fillibuster, Senate Majority Leader Harry Reid filed a procedural motion to limit debate and force a vote.  The procedural motion requires a 2/3rds majority vote (60 vote threshold).  Democrats hold a 55-45 edge in the Senate and have the numbers to confirm Hagel on a majority vote, but will need the support of five Republicans to clear the way for an up-or-down vote on Hagel. Right now, only two Republican Senators, Thad Cochran of Mississippi and Mike Johanns of Nebraska, have publically announced their support for Hagel’s nomination. Unless Mr. Reid can find another three Republican votes, he will not have the necessary 60 votes.  A vote on the Majority Leader’s procedural motion is expected to occur on Friday.   

http://online.wsj.com/article/SB10001424127887324432004578302633094527880.html

http://www.nydailynews.com/news/politics/senate-debate-chuck-hagel-confirmation-rages-article-1.1263605

http://www.senate.gov/artandhistory/history/minute/Cloture_Rule.htm