When Senate Majority Leader Harry Reid scheduled a Friday morning cloture vote on Chuck Hagel’s nomination to be Secretary of Defense, it seemed as though the former Senator’s confirmation was all but assured. But a short time ago, Huffington Post’s Sam Stein reported that at this time, Reid does not have the 60 votes needed to prevent a filibuster. So what gives?

According to a Republican source, roughly speaking, GOP Senators fall into a few camps when it comes to Hagel. The largest camp is comprised of Senators who have enough concerns about Hagel that they’re willing not only to vote against him, but to block a vote from happening by denying cloture. This group is led by freshman Sen. Ted Cruz, who has been persuasively arguing to his fellow Republicans – both publicly and privately – that they should at a minimum be willing to delay the Hagel nomination until he discloses information on the foreign sources of income that he may have received in the form of speaking fees as well as more information on the groups he’s spoken to and the content of his speeches.

A smaller group of Senators is on the bubble. That is, they are theoretically prepared to allow a final vote on Hagel by voting for cloture, but they are still frustrated by the Obama administration’s lack of cooperation in providing information related to the attack on a U.S. outpost in Benghazi last September. Sens. Lindsey Graham and John McCain, for instance, have been vocal in demanding more answers.

The source described the situation as “fluid.” The group currently on the bubble may be swayed to support Hagel if the administration satisfies their disclosure demands on Benghazi. But at the same time, they may ultimately oppose Hagel anyway if troubling new information surfaces related to Hagel’s foreign income and past speeches.

Democrats control 55 votes in the Senate, meaning that to thwart any filibuster, Reid would have to win over five Republicans. GOP Sens. Mike Johanns and Thad Cochran have said they would vote for Hagel and Susan Collins said she would at least be willing to vote for cloture. That would still leave him two votes short.

Leon Panetta, the current Secretary of Defense, was supposed to leave his job today. But, “a senior Defense Department official told ABC News that Panetta is prepared to stay in office until Hagel is confirmed.”

To be clear, fence-sitting Republicans could still come around to allowing a vote on Hagel tomorrow morning. There is concern within the Republican caucus about the precedent that would be set by filibustering a cabinet nominee.

But Democrats are certainly sweating quite a bit more than they were after Hagel cleared the Senate Armed Services Committee on Tuesday.