The Senate will vote Thursday to end debate on former Sen. Chuck HagelCharles (Chuck) Timothy HagelIntel chief: Federal debt poses 'dire threat' to national security Hagel: Trump is 'an embarrassment' Tax cut complete, hawks push for military increase 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 ReidGOP pushes to change Senate rules for Trump Trump presses GOP to change Senate rules Only thing Defense’s UFO probe proves is power of political favors 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 CruzConservatives balk over funding bill ahead of shutdown  Confirmation fight over Trump pick exposes blurred lines in GOP-LGBT activism GOP pushes to change Senate rules for Trump 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 McCainAfghanistan is our longest war ever and Congress has abandoned all responsibility Kremlin: ‘We have a long way to go’ before any breakthrough with US The GOP is Trump's party now MORE (R-Ariz.) and Lindsey GrahamLindsey Olin GrahamSenators introduced revised version of election cyber bill GOP senators push tougher sentencing for synthetic opioid Dems aim to turn ObamaCare hikes into election weapon 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 CollinsOvernight Health Care: House passes .3T omnibus | Bill boosts funds for NIH, opioid treatment | Senators spar over ObamaCare fix | 'Right to Try' bill heads to the Senate Winners and losers from the .3T omnibus Senators introduced revised version of election cyber bill MORE (R-Maine) has said she will not support a filibuster.

Two other Republicans, Sens. Mike JohannsMichael (Mike) Owen JohannsFarmers, tax incentives can ease the pain of a smaller farm bill Lobbying World To buy a Swiss company, ChemChina must pass through Washington MORE (Neb.) and Thad CochranWilliam (Thad) Thad CochranSenate bracing for possible long weekend All eyes on Paul with shutdown looming Cochran delivers farewell Senate address 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 AyotteAudit finds US Defense Department wasted hundreds of millions of taxpayer dollars US sends A-10 squadron to Afghanistan for first time in three years No, the US did not spend million on a gas station in Afghanistan 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 ClintonWhite House would like to see Biden ‘in the boxing ring’ in 2020 House Judiciary chair subpoenas DOJ for FBI documents The suit to make Electoral College more ‘fair’ could make it worse 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.