The vote on John Bolton (search) to be the next U.S. ambassador to the United Nations has been blocked, with Democrats trying to force the White House to release long-sought classified information about the controversial nominee, or perhaps to pick someone else for the job.

Republicans were not able to muster on Thursday the 60 votes needed to stop debate on Bolton's nomination despite support from two Democratic senators who had been instrumental in recent negotiations over judicial nominees.

Although Democrats claimed the move did not constitute a filibuster, Republicans said it sure looked like one.

"John Bolton, the very first issue we turned to, we got what looks to me like a filibuster," Frist said, adding that the matter soured the air of cooperation the two parties' centrists forged just days ago after months of wrangling over judges. "It certainly sounds like a filibuster ... it quacks like a filibuster."

"John Bolton, the very first issue we turned to, we got what looks to me like a filibuster," said Senate Majority Leader Bill Frist, R-Tenn. "It certainly sounds like a filibuster ... it quacks like a filibuster."

Senate Minority Leader Harry Reid said the vote against ending debate did not reflect on the nominee per se.

"We're not here to filibuster Bolton, we're here to get information on Bolton," Reid said.

The Senate voted 56-42 to move on to a confirmation vote, four shy of the tally needed for cloture. Democratic Sens. Mary Landrieu of Louisiana and Ben Nelson of Nebraska voted for the end to debate, but other Democrats argued they want more information on the nominee's requests for certain intelligence intercepts. Democratic Sen. Mark Pryor of Arkansas also voted for cloture.

Democrats had been threatening throughout the day to filibuster (search) Bolton, whom President Bush argues is the best person to help reform the U.N. They said they wanted more information from the State Department and National Security Agency even though both agencies argued they had shared enough. Debate will resume next month after lawmakers return from the Memorial Day recess.

"We should delay this until we see that information; it's a matter of right and wrong," Sen. Barbara Boxer (search), D-Calif., maintained at the start of a second day of Senate debate over Bolton. "It is right for us to get that information, it is wrong for the administration to withhold it."

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Democratic Sens. Christopher Dodd of Connecticut and Joseph Biden of Delaware, lead opponents to Bolton, asked other senators in a letter sent Thursday to support the delay. Dodd said on the Senate floor that Democrats would have no need to deny Bolton a vote if the Bush administration would just hand over the names that Bolton requested to see.

"When the chair and vice chair are deprived of seeing the names on an NSA intercept ... then we're not getting the information we need to make a decision," he said.

The NSA frequently provides officials with intercepts or wiretaps but generally blacks out the names of U.S. citizens. As undersecretary of state for arms control, Bolton asked to have some names revealed, which is not unusual. But Democrats want to know why.

Democrats said Wednesday they did not plan to mount a filibuster, or procedural delay, to indefinitely block the vote, but Biden and Dodd's letter demonstrated a change of heart.

"The refusal of the Executive Branch to provide information relevant to the nomination is a threat to the Senate's constitutional power to advise and consent. The only way to protect that power is to continue to demand that the information be provided to the Senate. The only means of forcing the administration to cooperate is to prevent a final vote on the nomination today. We urge to you vote no on cloture," reads the closing paragraph in the letter.

Still, the two insisted the vote was not a filibuster.

"We want to make clear that this is not a filibuster. It is a vote to protect the Senate's constitutional power to advise and consent to nominations," they wrote.

White House spokesman Scott McClellan said the administration was pleased that Republicans would revisit the vote after the recess but criticized Democrats for the newest delay.

"Just 72 hours after all the goodwill and bipartisanship, it is a shame to see the Democratic Senate leadership resort back to such a partisan approach," McClellan said. "This is a nominee that enjoys majority support."

Frist was the only Republican to vote against ending the delays, but he only did so because that gave him the procedural right to force the Senate to vote again on the issue.

Sens. Daniel Inouye, D-Hawaii, and Arlen Specter, R-Pa., did not vote.

"What you see here is partisanship and that is unfortunate," said Sen. George Allen, R-Va.

Bolton The 'Right Man for the Job'

The intercept material involves Bolton's use of government intelligence on Syria and instances in which he asked for names of fellow U.S. officials whose communications were secretly picked up by a spy agency.

The top Democrat on the Senate Intelligence Committee, Jay Rockefeller, on Thursday suggested Bolton may have improperly used that information, but conceded he had done nothing improper by asking for the names in the first place.

Boxer also accused Bolton of misleading the Senate committee that wrangled over Bolton's nomination for weeks without offering him its endorsement.

"John Bolton did not tell the truth to the Foreign Relations Committee," on several points, Boxer alleged. "If nothing else I've said matters ... you ought to care about telling the truth to a committee of the United States Senate," Boxer told other senators.

Republicans, in turn, said a strong voice and hand is needed to force U.N. reform, particularly in the wake of scandals that have shaken the foundation of the organization, such as the Oil-for-Food (search) scheme.

"John Bolton has the fortitude to stand up for what is right, fight the good fight and to prevail," said Sen. John Ensign, R-Nev. "Secretary [of State Condoleezza] Rice called Bolton a 'tough minded diplomat' — that's exactly what the U.S. needs at the U.N."

Sen. John McCain, a key figure in this week's judicial filibuster compromise, took to the floor to speak in support of Bolton, joking that he may have "particular sympathy" for the nominee given the charges that, among other things, Bolton's temperament should disqualify him from taking the post.

McCain made light of his own temper, sarcastically suggesting he's always been even-tempered himself and "not involved" in any controversial issues. But then he turned to a more serious tone.

"Is there anybody that doesn't believe the U.N. is in need of reform?" the Arizona Republican asked. "The U.N. needs the presence of a tough, hard, dedicated individual … I think we realize it's time to move ahead with the people's business."

The State Department on Thursday said it has cooperated "extensively" with congressional requests regarding Bolton.

State Department spokesman Richard Boucher noted Thursday that hundreds of hours have been spent producing "extensive documents" on the issue, while 36 interviews have been conducted and 175 written questions answered.

"We think all this review puts the Senate in a position to make its judgment on John Bolton's nomination," Boucher said. "Once again, we reiterate the secretary and the president believe he's the right man for the job. We hope to see him at the United Nations very soon. "

But Boucher said he could not respond to all the document requests, including internal deliberations on testimony given to Congress.

"We think that providing that kind of internal deliberations on a document that was fully cleared would have a chilling effect on our ability to have discussions like that in the future," and noting that some of the information was already cleared by the Senate Foreign Relations Committee.

Voinovich: Bolton a 'Kiss-Up, Kick-Down' Guy

Bolton is currently one of Bush's most hawkish foreign policy advisers. Bush nominated him in March to succeed John Danforth (search) as U.N. ambassador.

So far, one Republican has spoken against Bolton. Sen. George Voinovich (search), R-Ohio, said Bolton would set back the U.S. goal of reforming the United Nations and lacks the diplomatic touch for the sensitive job of ambassador.

Voinovich, who agreed to vote for an end to debate, implored senators to think hard before voting to approve Bolton. His surprisingly strong opposition forced a delay of last month's planned Foreign Relations Committee vote on Bolton, and the panel subsequently denied Bolton its customary endorsement.

In an interview with FOX News on Thursday, Voinovich called Bolton a "kiss-up, kick-down kind of guy" who got along well enough with colleagues on his level or above but not with those under him in rank.

"There's a way to do it and there's a way not to do it," Voinovich said in regard to reforming the United Nations, adding that particularly within the last few years, Bolton has "just gone off on his own mission."

Voinovich noted that 102 former ambassadors and others say Bolton is not the best man to send to the world body "at a time when the United States of America wants to change the world's opinion and get our allies on board so they can help us wage these wars and pay for these wars and also get the changes we need in the United Nations."

Saying Bolton "pales" in comparison to former U.S. ambassador to the United Nations, John Negroponte, the senator suggested that individuals like Bush adviser Karen Hughes or Marc Grossman, former undersecretary for political affairs at the State Department, would be great choices for the top U.S. diplomatic post at the international body. Hughes has been nominated to head the new Muslim World Outreach Policy Coordinating Committee in the State Department.

"I think Karen, whose very close to the president, would do an outstanding job at the United Nations," Voinovich said. "There are plenty of other people around."

FOX News' Julie Asher, Megyn Kendall, Liza Porteus, Teri Schultz and The Associated Press contributed to this report.