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“I’ll cross that bridge when I come to it,” he told reporters outside the Senate chamber. “My position right now is I want answers to the questions.”

Chairman Carl Levin, Michigan Democrat, said Mr. Hagel has cooperated with the committee’s rules and is qualified for the job.

“The president needs to have a secretary of defense in whom he has trust, who will give him unvarnished advice, a person of integrity and one who has a personal understanding of the consequences of decisions relative to the use of military force,” Mr. Levin said on the Senate floor.

Mr. Levin said Mr. Hagel has the full support of five previous defense secretaries and that he served courageously in the Vietnam War. Mr. Hagel would be the first former enlisted man to serve as defense secretary.

Although they may seem arcane, document requests can be powerful weapons against nominees.

Americans for a Strong Defense, a group that opposes Mr. Hagel’s nomination, accused Senate Democrats of hypocrisy Wednesday for insulating the nominee from Republicans’ request for records, noting the party employed a wide range of delay tactics to thwart some of President George W. Bush’s nominees.

They pointed to successful efforts to block John R. Bolton as ambassador of the United Nations, after Mr. Bush submitted his name to keep him on the job in 2006.

Miguel A. Estrada, an accomplished lawyer known to possess conservative views, withdrew his name from consideration for the U.S. Court of Appeals for the District of Columbia after senators stirred controversy from 2001 to 2003 by calling for legal memos that Mr. Estrada composed during his time at the Department of Justice.

“There’s certainly a history of calling for disclosure for nominees that have gone before the Senate,” said Ryan Williams, the organization’s spokesman.

Despite these precedents, “it’s very unusual to do this with a major nomination,” said Thomas E. Mann, a senior fellow at the Brookings Institution.

As of now, Mr. Hagel and Mr. Brennan face roadblocks — and Jacob “Jack” Lew, Mr. Obama’s nominee to be the Treasury Department secretary, could also may have to overcome obstacles if he doesn’t provide more information about his investment history.

Mr. Hagel’s nomination was cleared through the Armed Services Committee on Tuesday on a party-line vote.

Two Republicans have said they would support his nomination, while others have said they would vote against him but wouldn’t take part in a filibuster.

“I wish that President Obama had made a different choice for this critical position, but he is entitled to have this nominee receive a direct vote on the Senate floor,” said Sen. Susan M. Collins, Maine Republican.