His supporters, which included several Democrats, said Mukasey is the best prospect lawmakers are going to get in the waning months of a Bush administration unwilling to nominate anyone else.
"This is the only chance we have," said Sen. Dianne Feinstein, D-Calif.
But members of her own party didn't agree that Mukasey is better than somebody appointed and not subject to Senate confirmation. Mukasey, his opponents argued, said he didn't know if waterboarding is illegal torture and put the onus on Congress to pass a law against the practice.
"This is like saying when somebody murders somebody with a baseball bat and you say, 'We had a law against murder but we never mentioned baseball bats,'" said Judiciary Committee Chairman Patrick Leahy, D-Vt. "Murder is murder. Torture is torture."
Being better than former Attorney General Alberto Gonzales or an acting attorney general is not enough qualification for the job, added Sen. Edward M. Kennedy, D-Mass.
"The next attorney general must restore confidence in the rule of law," Kennedy said. "We cannot afford to take the judgment of an attorney general who either does not know torture when he sees it or is willing to look the other way."
The debate and impending vote capped 10 months of scandal and resignations that left the Justice Department leaderless after Gonzales resigned in September. Mukasey's chief Democratic patron, Sen. Chuck Schumer, D-N.Y., drove the probe into the purge of federal prosecutors that helped push Gonzales out.
The debate came after a tense day of negotiations that at one point featured Majority Leader Harry Reid threatening to postpone Mukasey's confirmation until December. His confirmation had long been virtually assured despite the debate over his refusal to call waterboarding torture.
To win confirmation, Mukasey has promised to enforce any anti-waterboarding law passed by Congress, where, his Republican supporters say, responsibility for such policies lie.
Mukasey's Democratic opponents say he is being disingenuous because any such law would likely be vetoed by President Bush.
Waterboarding, used by interrogators to make someone feel as if he is going to drown, is banned by domestic law and international treaties. But U.S. law applies to Pentagon personnel and not the CIA. The administration won't say whether it has allowed the agency's employees to use it against terror detainees.
"The United States will not be viewed kindly if we confirm as chief law enforcement officer of this country someone who is unwilling or unable to recognize torture when he sees it," said Sen. Dick Durbin of Illinois, the Senate's No. 2 Democrat.
Mukasey has called waterboarding personally "repugnant," and in a letter to senators said he did not know enough about how it has been used to define it as torture. He also said he thought it would be irresponsible to discuss it since doing so could make interrogators and other government officials vulnerable to lawsuits.
"He felt that he could not make that pronouncement without placing people at risk to be sued or perhaps even criminally prosecuted," said Sen. Arlen Specter of Pennsylvania, the ranking Republican on the Senate Judiciary Committee.