For the second time in a month, Republicans failed to muster the votes necessary to end the debate on John Bolton's ( search) nomination for ambassador to the United Nations ( search) and move him to a final up-or-down vote.

This time, the final tally was 54-38 with eight senators not voting. Sens. Mary Landrieu of Lousiana, Ben Nelson of Nebraska and Mark Pryor of Arkansas, the same three Democrats who defected last time, did so again. Republican Sen. George Voinovich of Ohio, one of Bolton's most vocal critics, voted for cloture in May, but opposed the nominee this time. The vote was six shy of the threshold needed to go to a final vote in which majority would rule.

Afterwards, Senate Majority Leader Bill Frist, R-Tenn., accused Democrats of being unwilling to compromise.

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"Some on the other side of the aisle are obstructing a highly qualified nominee and I believe by not allowing him to assume this position yet are doing harm to our country," Frist said.

One Republican senator acknowledged to reporters that he is concerned that if Bolton ever gets to the U.N., he might be regarded by other ambassadors as "damaged goods."

"That is a legitimate concern though that you bring up and I would hope that the president will stand by John Bolton and keep fighting for him," Sen. George Allen, R-Va., said.

Sen. Chris Dodd of Connecticut, a leading Democrat in the battle against Bolton, suggested after the vote that any number of "good, strong, tough conservatives" could be confirmed more easily than Bolton.

"I would strongly encourage the administration tonight to move on, to give us another nominee, someone who the administration can support, that we can support here," Dodd said.

President Bush has said Bolton, who has a history of criticizing the United Nations, is the best chance to lead an effort to overhaul the world body's bureaucracy and make it more accountable. Critics say Bolton, who has been accused of mistreating subordinates, would hurt U.S. efforts to work with the U.N. and other countries.

In a news conference with leaders of the European Union at the White House before the latest vote on Bolton, Bush urged Senate Democrats to abandon the filibuster they have used to block the nominee for the last month.

"I think Mr. Bolton ought to get an up or down vote on the Senate floor. That's my call to the Senate," Bush said. "If they're interested in reforming the United Nations, they ought to approve John Bolton."

Earlier in the day, Sen. Joseph Biden ( search), ranking minority member on the Senate Foreign Relations Committee and the leader of the filibuster against Bolton, spoke with White House Chief of Staff Andrew Card in an attempt to reach a compromise on the two outstanding document requests on which Democrats have based their objection to an up-or-down vote on Bolton.

Up to now, the Bush administration has flatly rejected requests for early drafts of Bolton's House testimony on Syria that was delivered two years ago. On Monday, Card offered to make headway on the Syria issue if Democrats would drop their demands to see 36 names in National Security Agency documents that Bolton had requested and was allowed to see.

But during debate before the vote, Biden of Delaware said neither demand is negotiable.

"The vote is about whether or not the United States Senate will allow the president to dictate to a co-equal branch of government how we, the United States Senate, are to fulfill our constitutional responsibility under the advice and consent clause," he said.

"We continue to work in good faith to address any concerns, but it's clear that the Democratic leadership isn't interested in more information; they're only interested in blocking his nomination," White House press secretary Scott McClellan said earlier in the day.

If neither side caves, Bush has the option of bypassing lawmakers and appointing the Undersecretary of State for Arms Control and International Security to the post while Congress is on its July 4 break despite a warning from the top Senate Democrat not to give Bolton a recess appointment.

"The president will have to make a decision whether he wants to send this flawed candidate to the United Nations under an also questionable constitutional measure, which is being tested in the courts as we speak," Senate Minority Leader Sen. Harry Reid, D-Nev., said.

The chairman of the Senate Intelligence Committee, Sen. Pat Roberts, R-Kan., said it would be better if Bush left the fight up to the Senate for fear of compromising Bolton's influence at the world body.

While a recess appointment would last through to the start of the next session of Congress after the yearlong appointment — in this case January 2007 — administration officials have so far said talks of a recess appointment are premature since the current session of Congress still has two weeks before the Independence Day recess.

No president has used a recess appointment for a U.N. ambassador since 1970, when the Senate Historian's Office began keeping records, according to one of the historians, Betty Koed. Presidents have occasionally made recess appointments of ambassadors to countries, including President Clinton's 1996 appointment of former Sen. Wyche Fowler, D-Ga., to be ambassador to Saudi Arabia.

FOX News' James Rosen and The Associated Press contributed to this report.