The Senate will vote Thursday to end debate on former Sen. Chuck HagelCharles (Chuck) Timothy HagelOvernight Defense: Latest on historic Korea summit | Trump says 'many people' interested in VA job | Pompeo thinks Trump likely to leave Iran deal Should Mike Pompeo be confirmed? Intel chief: Federal debt poses 'dire threat' to national security MORE's nomination to be Defense secretary, a vote headed for failure. 

Sixty votes would be needed to end debate and move to a final up-or-down vote on Hagel, but Democrats do not have the necessary support. 

Republican leaders in the Senate have told Senate Democrats they will withhold enough votes to prevent a 60-vote majority, according to a Senate Democratic leadership aide. And Republicans left their party lunch in the Capitol on Thursday saying they had enough support to block a vote this week because they felt they were not given enough time to consider Hagel's nomination.

Senate Majority Leader Harry ReidHarry Mason ReidAmendments fuel resentments within Senate GOP Donald Trump is delivering on his promises and voters are noticing Danny Tarkanian wins Nevada GOP congressional primary MORE (D-Nev.) had set the vote for Friday, but moving it up to Thursday would allow senators to conclude their business and start a long recess early. The Senate is set to be out next week for Presidents Day recess. 

The move means Hagel will not be confirmed before a NATO meeting next week about the Afghanistan war. Retiring Defense Secretary Leon Panetta has pledged to stay on duty until Hagel is confirmed. 

This is the first time a nominee for the top Pentagon job has been subject to a filibuster, a fact that highlights how contentious Hagel's nomination has become. Hagel's views on Iran, Iraq and Israel led to a fiery debate over his nomination. He went through a rough confirmation hearing last week, enduring tough questions from Republican senators and turning in an uneven performance. 

Since then, Republicans have demanded more information about speeches the nominee gave and his compensation for them. Sen. Ted CruzRafael (Ted) Edward CruzMcCain calls on Trump to rescind family separation policy: It's 'an affront to the decency of the American people' Cruz announces bill to end separation of immigrant families The Hill's 12:30 Report — Sponsored by Delta Air Lines — Furor grows over child separation policy MORE (R-Texas) at a hearing this week suggested the speeches were given to extreme or radical groups, a statement some Democrats have criticized.

The White House blasted the Republican filibuster attempt as "unconscionable."

"We urge the Republicans in the Senate to drop their delay," White House deputy press secretary Josh Earnest told reporters aboard Air Force One as the president headed to Georgia. "There is a clear majority in the United States Senate for Sen. Hagel's confirmation. These delaying tactics are unconscionable, and they should end right away."

"Next week there is a defense ministerial meeting in Brussels, where the U.S. will meet with our allies, who are making important contributions to our effort in Afghanistan, to talk about the transition in Afghanistan," Earnest said. "We need our new defense secretary to be there. It does not send a favorable signal for Republicans in the United States Senate to delay a vote on the president's nominee, a nominee who's a member of their own party. It's difficult to explain to our allies exactly why that's happening."

Reid's decision to hold the Thursday night vote capped a day of maneuvering by both parties. 

Reid stepped up pressure Thursday for Republicans to allow an up-or-down vote, arguing it would leave the U.S. without a Defense secretary. 

“We, at 12 o’clock today, do not have a secretary of Defense,” Reid said on the Senate floor Thursday morning. “It is shocking that our Republicans colleagues would leave our nation without a secretary of Defense with all the things going on and when we’re in a war.”

Multiple senators — including Sens. John McCainJohn Sidney McCainTrump plan to claw back billion in spending in peril McCain calls on Trump to rescind family separation policy: It's 'an affront to the decency of the American people' Senate passes 6B defense bill MORE (R-Ariz.) and Lindsey GrahamLindsey Olin GrahamTrump digs in amid uproar on zero tolerance policy Senate passes 6B defense bill Justice IG says report doesn’t assess ‘credibility’ of Russian probe MORE (R-S.C.) — said they only would vote to proceed with confirmation after the Presidents Day recess. 

“There’s a good many of us who believe tomorrow is ridiculous because he just came out of committee two days ago,” Graham said of ending debate on Hagel on Friday. “But when we come back, I’d feel very comfortable, unless something really stunning comes out, to go to vote.”

All 55 senators who caucus with Democrats are expected to support Hagel, and Sen. Susan CollinsSusan Margaret CollinsTrump plan to claw back billion in spending in peril Romney backs Laura Bush on border: 'We need a more compassionate answer' Amnesty International rips family separation policy: 'This is nothing short of torture' MORE (R-Maine) has said she will not support a filibuster.

Two other Republicans, Sens. Mike JohannsMichael (Mike) Owen JohannsMeet the Democratic sleeper candidate gunning for Senate in Nebraska Farmers, tax incentives can ease the pain of a smaller farm bill Lobbying World MORE (Neb.) and Thad CochranWilliam (Thad) Thad CochranTodd Young in talks about chairing Senate GOP campaign arm US farming cannot afford to continue to fall behind Mississippi Democrat drops Senate bid MORE (Miss.), support Hagel's nomination. But only one of them has signaled so far he will vote for cloture.

A Johanns aide said that the Nebraska senator will vote to end debate, but an aide to Cochran told The Hill on Thursday that he has not said anything specific on the cloture vote.

Collins said Thursday that she was not lobbying her colleagues to vote for cloture.

“Everybody has to make his or her own decision,” she said.

Democrats spent part of Thursday searching for more Republican votes to reach 60, and were hopeful that the White House’s response on Benghazi to McCain, Graham and Sen. Kelly AyotteKelly Ann AyotteErnst, Fischer to square off for leadership post The Hill's Morning Report: Koch Network re-evaluating midterm strategy amid frustrations with GOP Audit finds US Defense Department wasted hundreds of millions of taxpayer dollars MORE (R-N.H.) might convince them to vote for cloture.

McCain has linked his vote to end debate on Hagel to receiving information from the administration on why the military did not respond to the terrorist attack last year on the U.S. Consulate in Benghazi, Libya. On Thursday, he said that his concerns over Benghazi were "largely satisfied" by a letter sent from the White House on Wednesday.

But McCain declined to say how he would vote on cloture, saying that negotiations were ongoing to address the concerns other senators had over Hagel's financial disclosures.

In the letter, obtained by The Hill, the White House wrote that then-Secretary of State Hillary ClintonHillary Diane Rodham ClintonKoch brothers group won't back Stewart in Virginia Giuliani says his demand for Mueller probe to be suspended was for show Poll: GOP challenger narrowly leads Heitkamp in North Dakota MORE called the Libyan president the night of the attack. The GOP senators had asked whom Obama had spoken with in the Libyan government that night.

Reid said it would reflect poorly on the United States that a secretary of Defense would not be representing the country at the meeting in Brussels.

“Republicans are telling our troops, ‘Well, you can have a leader later. The meeting in Brussels doesn’t really matter,’ ” Reid said.

— Published at 10:27 a.m. and updated at 3:19 p.m.

Carlo Munoz contributed.