The Senate will vote Thursday to end debate on former Sen. Chuck HagelCharles (Chuck) Timothy HagelOvernight Defense: US, Russia tensions grow over nuclear arms | Highlights from Esper's Asia trip | Trump strikes neutral tone on Hong Kong protests | General orders ethics review of special forces Five takeaways from Pentagon chief's first major trip Esper given horse in Mongolia as US looks for new inroads against China 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 Reid2020 Democrats fight to claim Obama's mantle on health care Reid says he wishes Franken would run for Senate again Panel: How Biden's gaffes could cost him against Trump 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 CruzTrump moves forward with F-16 sale to Taiwan opposed by China The Hill's Campaign Report: Battle for Senate begins to take shape O'Rourke says he will not 'in any scenario' run for Senate 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 McCainFighter pilot vs. astronaut match-up in Arizona could determine control of Senate The Hill's Morning Report — Recession fears climb and markets dive — now what? Trump makes rare trip to Clinton state, hoping to win back New Hampshire MORE (R-Ariz.) and Lindsey GrahamLindsey Olin GrahamGraham warns Trump on Taliban deal in Afghanistan: Learn from 'Obama's mistakes' Appropriators warn White House against clawing back foreign aid Trump meets with national security team on Afghanistan peace plan 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 CollinsCook Political Report moves Susan Collins Senate race to 'toss up' The Hill's Morning Report — Trump and the new Israel-'squad' controversy Trump crosses new line with Omar, Tlaib, Israel move 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 CochranBiden has a lot at stake in first debate The Hill's Morning Report — Trump turns the page back to Mueller probe Trump praises Thad Cochran: 'A real senator with incredible values' 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 AyotteTrump makes rare trip to Clinton state, hoping to win back New Hampshire Key endorsements: A who's who in early states Sinema, Gallagher fastest lawmakers in charity race 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 ClintonLewandowski on potential NH Senate run: If I run, 'I'm going to win' Fighter pilot vs. astronaut match-up in Arizona could determine control of Senate Progressive Democrats' turnout plans simply don't add up 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.