Senate Republicans on Thursday pummeled former Sen. Chuck Hagel of Nebraska, President Obama's nominee for defense secretary, at a confirmation hearing that left Hagel bloodied enough to raise questions about his confirmation.

Hagel frequently struggled to defend himself, stumbling over even basic defense policy questions from former colleagues. Despite days of preparation, Hagel acknowledged, he still lacks a complete understanding of specific military programs.

"I, if confirmed, intend to know a lot more than I do," Hagel said. "I will have to."

Obama once asked Hagel why he would be uniquely qualified to become defense secretary, Hagel told the committee. He said he told the president, "I'm not."

Some Republican aides now suggest that the poor performance may cost Hagel the job.

"He might not even get out of committee," one aide told The Washington Examiner. "He was completely unprepared, bordering on incompetent."

Obama said he tapped Hagel, a Republican who left the Senate after his second term in 2009, because Hagel is independent-minded with views both "in and out of the box."

GOP lawmakers denounced what they described as Hagel's left-of-center views on Israel, Iran and the size of the U.S. military. They quizzed Hagel repeatedly about past remarks that have turned his nomination process into the most contentious thus far for the Obama administration.

Even before Obama nominated him, Hagel was being savaged in television ads run by outside interest groups that took him to task for once claiming that "the Jewish lobby intimidates a lot of people" in Congress. He was also attacked as anti-gay and for aligning himself with the Global Zero nuclear disarmament program that advocates drastic reduction in nuclear weapons.

Hagel struggled to defend himself but stumbled over even basic defense policy matters. Senate Armed Services Committee Chairman Carl Levin, D-Mich., twice had to correct Hagel's statements on the U.S. position on Iran pursuing nuclear weapons.

Hagel, who as a senator voted against designating Iran's Revolutionary Guard a terrorist organization, angered lawmakers with a claim that Iran has "an elected, legitimate government."

A number of committee Republicans had made their opposition to Hagel's nomination clear even before the hearing. But Hagel's performance may have cost him support from those Republicans still open to considering him.

"Though I respect Sen. Hagel, his record to date demonstrates that he would be a staunch advocate for the continuation of the misguided policies of the president's first term," said Sen. James Inhofe, R-Okla., the committee's top Republican who had already planned to vote against Hagel.

Hagel's nomination is not necessarily doomed. He needs the support of only five Senate Republicans to reach the 60-vote threshold needed for confirmation, since Democrats already control 55 votes.

Only one GOP Senator, Thad Cochran of Mississippi, has pledged to back Hagel.

Sen. John McCain, R-Ariz., who, like Hagel, is a Vietnam War veteran, lambasted his former colleague for voting against the 2007 troop surge in Iraq that is credited as a success.

McCain quoted Hagel's assessment that the surge was "the most dangerous foreign policy blunder since Vietnam," and tried to get Hagel to say he was wrong. But Hagel said he was describing the entire Iraq War, not just the surge, and refused to reassess his original answer.

"I'll defer that judgement to history," Hagel told McCain.