McCain pressed Hagel on whether he was right or wrong about his opposition to President George W. Bush's decision to send an extra 30,000 troops to Iraq in 2007 at a point when the war seemed in danger of being lost. Hagel, who voted to authorize military force in Iraq, later opposed the conflict, comparing it to Vietnam and arguing that it shifted the focus from Afghanistan.
"Were you right? Were you correct in your assessment?" McCain asked.
"I would defer to the judgment of history to sort that out," Hagel said as the two men talked over each other.
"The committee deserves your judgment as to whether you were right or wrong about the surge," McCain insisted.
Unable to elicit a simple response, McCain said the record should show that Hagel refused to answer. And he made it clear that he would have the final word -- with his vote, which he said would be influenced by Hagel's refusal to answer yes or no.
"I think history has already made a judgment about the surge, sir, and you're on the wrong side of it," he said.
Hagel was the lone witness in a jam-packed hearing room at a session that could be crucial in determining whether he will win Senate confirmation and join Obama's second-term national security team. He spoke out forcefully for a strong military while trying to explain 12 years of Senate votes and numerous statements.
"No one individual vote, no one individual quote or no one individual statement defines me, my beliefs, or my record," Hagel said in his opening statement. "My overall worldview has never changed: that America has and must maintain the strongest military in the world, that we must lead the international community to confront threats and challenges together, and that we must use all tools of American power to protect our citizens and our interests."
Hagel, 66, would be the lone Republican in Obama's Cabinet, the first Vietnam veteran to be defense secretary and the first enlisted man to take the post. That last point was highlighted by Levin.
"It would be a positive message for our soldiers, sailors, airmen and Marines in harm's way around the world to know that one of their own holds the highest office in the Department of Defense and that he has their backs," Levin said.
Hagel has the announced backing of about a dozen Democrats and the tacit support of dozens more who are unlikely to embarrass the president by defeating his Cabinet pick. One Republican -- Sen. Thad Cochran of Mississippi -- has said he will vote for his former colleague.
Eight Republicans, including four members of the Armed Services panel, have said they will oppose Hagel's nomination. Dan Coats of Indiana, who served with Hagel in the Senate, and Marco Rubio of Florida announced their opposition on Thursday.
Democrats hold a 55-45 advantage in the Senate and a 14-12 edge on the committee.