Reid took to the Senate floor on Thursday morning, building pressure on Republicans to back off of their threats. He added that the letter sent from the White House answers "all their questions."

"This isn't a high school getting ready for a football game or some play that's being produced at the high school," he also said. "This is, we're trying to confirm somebody to run the defenses of our country, the military of our country."

Outgoing Defense Secretary Leon Panetta says he will remain in his position until a defense nominee is "sworn into office," a senior Pentagon official said Thursday.

Administration officials and Congressional Democrats said they were on the phone late into the night Wednesday discussing how to get Republican votes. The sources said the administration had been told they did not have enough GOP votes to gain the necessary 60 to stop a filibuster.

Meanwhile, some questioned whether Hagel would withdraw his nomination. But one senior administration official said that idea is "insane."

Referring to the GOP, the official said, "No one knows what they really want. There is nothing real to be had."

"They wanted testimony from (former Secretary of State) Hillary Rodham Clinton and Leon Panetta and they got it...there is nothing real to be had," the official continued.

Hagel's brother Tom, a law professor who's in constant contact with his brother, also said Hagel will not withdraw his name.

"Knowing him, not only will he not withdraw, but he will be motivated to fight harder," he said.

Asked Wednesday in a press conference whether the GOP was moving goal posts on the issue, Graham gave a firm "no."

"I'm gonna hit you, and keep hitting you," he vowed. "Absolutely. You're not going to get away without answering the basic questions. Did you make a phone call on September 11th to any Libyan government official using the weight and the voice of the president of the United States to help these people in their time of great need."

Speaking aboard Air Force One, however, White House Deputy Press Secretary Josh Earnest stressed earlier Thursday a sense of urgency in filling the new defense secretary position.

"It is difficult to explain to our allies why exactly that is happening. It also sends a signal to our men and women in uniform who are currently deployed around the world and who are currently serving in the frontlines of Afghanistan and are taking fire today," he told reporters. "They need a new secretary of defense. So we urge Republicans in the Senate to drop their delay."