As Senate Majority Leader Harry Reid set a cloture vote for Thursday afternoon at 4:15 pm ET, the White House is trying to answer Republican concerns and Vice President Biden is making calls to ex-GOP Senate colleagues in an effort to save Chuck Hagel's nomination for defense secretary. 

Republicans are threatening to filibuster Hagel's nomination and require 60 votes to overcome cloture, if they do not receive more information on Hagel's speeches and finances. Sens. John McCain (R-AZ), Lindsey Graham (R-SC), and Kelly Ayotte (R-NH) sent a Feb. 12 letter to the White House requesting more information on the attacks in Benghazi and are tying Hagel's nomination to it. 

Hagel has 57 votes -- 55 Democrats and two Republicans -- but would need three Republicans to vote for cloture, to end debate on his nomination, in order for it to proceed to a final up-or-down confirmation vote. The White House believes with Susan Collins (R-ME), Hagel has 58 votes for cloture.

"The Administration has repeatedly made clear its commitment to understanding the facts and circumstances surrounding the September 11-12, 2012 attack on our diplomatic mission in Benghazi...," White House Counsel Kathryn Ruemmler wrote in response to McCain, Graham, and Hagel.

READ THE FULL LETTER HERE.

Ruemmler also writes that the administration has begun to implement "each and every one" of the Accountability Review Board recommendations.  

"This intensive response, which was directed by the President, included 13 meetings of interagency Principals and Deputies within a week of the attack and included continuous outreach by senior administration officials to the Government of Libya, including by the President and members of his Cabinet," Ruemmler wrote.

Republicans have questioned the level of involvement of President Obama in the handling of the aftermath of Benghazi. In response to a specific question from McCain, Graham, and Ayotte, Reummler writes, "Secretary Clinton called Libyan President Magariaf on behalf of the President on the evening of September 11, 2012 to coordinate additional support to protect Americans in Libya...The President spoke to President Magariaf on the evening of September 12." 

She ends the letter with: "We continue to urge the full Senate to act swiftly and confirm former Senator Hagel as the next Secretary of Defense."

In the Senate, McCain said Thursday there is an effort underway to negotiate a way to get more information and get Hagel a clean up-or-down vote.

"We are working on and having negotiations now trying to smooth this thing out and get it done," McCain said. "We're working on trying to get a path forward to having the questions answered and the vote and Hagel getting his vote."

NATO defense ministers are meeting next week in Brussels, and the administration would like to have Hagel in place to attend. Reid had said earlier Thursday he would set the cloture vote on Hagel's nomination for Friday morning and an up-or-down vote Saturday before moving it up to Thursday afternoon.

"It's critical that we get our new national security team confirmed as soon as possible," said a White House official, per Kristen Welker. "When we have 66,000 American troops serving in Afghanistan, face the looming threat of sequestration, and are dealing with continued North Korean intransigence, it's irresponsible not to move forward to confirm Chuck Hagel. There are real consequences to this kind of unprecedented political posturing against a Defense Secretary nominee - consequences that are dangerous to our national security.

But Republicans want a further delay until after the Senate's break next week. 

No Defense Secretary has ever been filibustered and just two cabinet secretary nominees, aside from Hagel, have been. But McCain harkened back to the failed nomination of John Tower in 1989.

"I have said all along that we had to have the concerns of Senators addressed," McCain said, "and I'm hopeful we can get those concerns addressed and still move forward with a 51-vote vote, because we have never required 60 votes of a Defense Secretary. But I would remind you that in the case of John Tower -- and I was here when you were teenagers -- John Tower, nominated on Dec. 16, 1988. [On] March 10, 1989, the Senate rejected his nomination. I was here, while the Democrats stalled his nomination for three months. So please, don't give me that argument about how we're holding things up."

Tower was rejected 53-47. It was not by a filibuster, but Democrats controlled the chamber. Three Democrats voted for Tower; one Republican voted against.

Graham said he would support cloture after the recess "unless there's some bombshell."

NBC's Kristen Welker, Mike Viqueira, and Bob Constantini contributed to this report.

This story was originally published on Thu Feb 14, 2013 2:17 PM EST