The candidates argued that Mukasey's silence suggests he won't stand up to the Bush administration.
"We cannot send a signal that the next attorney general in any way condones torture or believes that the president is unconstrained by law," said Sen.of New York.
The Democratic front-runner said Mukasey has had plenty of chances to clarify his answers and state his opposition to interrogation techniques. "His failure to do so leaves me no choice but to oppose his nomination," Clinton said.
Her statement, issued after other Democratic contenders declared their opposition to Mukasey, came as he prepared to deliver his answer on the question to the Senate Judiciary Committee. The panel must vote on whether to advance the nomination to the full Senate.
Mukasey is a longtime friend of Republican hopeful Rudy Giuliani and was advising his campaign until President Bush picked him to serve as attorney general.
Clinton's chief rival, Sen.of Illinois, said he will vote against the nomination.
"We don't need another attorney general who believes that the president enjoys an unwritten right to secretly ignore any law or abridge our constitutional freedoms simply by invoking national security. And we don't need another attorney general who looks the other way on issues as profound as torture," Obama said.
Several Democrats, including Senate Majority Leader Harry Reid of Nevada, have said they would vote against Mukasey if he does not equate waterboarding, the method that simulates drowning, with torture banned under domestic and international law.
"Anyone who thinks that waterboarding is not torture, is not fit and will not have my support to be attorney general," said another candidate, Sen.of Delaware.
A member of the Senate Judiciary Committee, Biden also circulated a letter Tuesday urging his colleagues to support legislation he introduced in July that would prohibit U.S. personnel from engaging in waterboarding and other torture techniques.
Sen.of Connecticut said Sunday that he would vote against Mukasey's nomination.