A defiant group of senators refused to continue down the path of a widely unpopular immigration reform bill Thursday, putting up a roadblock on a procedural debate and squeezing out any time left to work on one of President Bush's top domestic priorities.

On the cloture vote — the test to end debate and move to passage — the Senate voted 46-53 not to carry the motion. Sixty votes were needed for forward progress.

The tally is a turnaround of 18 votes from two days earlier. For varying reasons, six Democrats and 12 Republicans changed their votes to 'no' from a Tuesday vote that allowed the Senate to take up amendments on the bill. No one changed their votes to 'yes.'

Democrats who changed their votes were: Sens. Jeff Bingaman of New Mexico, Sherrod Brown of Ohio, Tom Harkin of Iowa, Ben Nelson of Nebraska, Mark Pryor of Arkansas and Jim Webb of Virginia.

Republicans who changed their votes were: Minority Leader Mitch McConnell of Kentucky, and Sens. Kit Bond of Missouri, Sam Brownback of Kansas, Richard Burr of North Carolina, Norm Coleman of Minnesota, Susan Collins of Maine, Pete Domenici of New Mexico, John Ensign of Nevada, Lisa Murkowski and Ted Stevens of Alaska, George Voinovich of Ohio and John Warner of Virginia.

Click here to see how your senators voted.

The vote most likely puts an end to efforts to fix the country's porous borders and legalize the 12 million unlawful immigrants now living inside the U.S. The issue is so volatile, lawmakers won't want to touch it before the next presidential election.

Still, Sen. Ted Kennedy, D-Mass., who co-authored the legislation along with Arizona Republican Sen. Jon Kyl, said the bill would live to see another day.

"The United States Senate was created just for this kind of issue. ... You cannot stop the march for progress in the United States, and on this issue I have every hope and every expectation that we will ultimately be successful.

Senate Majority Leader Harry Reid, D-Nev., also tried to find a silver lining.

"Even though the vote is really disheartening to me in many ways, I think as a result of this legislative work that we've done in the last several months, there have been friendships developed that weren't there before," Reid said after the vote ended.

He added that he was hopeful those friendships could be used to build coalitions to resurrect portions of the bill that the majority does want passed.

As day broke Thursday ahead of a vote to cut off debate, it appeared only the White House believed the bill could be saved. An increasing number of senior Senate aides and outside lobbyists who support the bill reconciled themselves to defeat.

Bush, making a last-ditch bid to salvage the bill, called senators early Thursday morning to urge their support. Homeland Security Secretary Michael Chertoff and Commerce Secretary Carlos Gutierrez approached senators as they entered and left the chamber shortly before the vote.

Afterward, Bush, whose job approval rating dropped to 31 percent in the latest FOX News-Opinion Dynamics poll out Thursday, said he was sorry the Senate could not reach agreement on the bill.

Click here to read the latest FOX News-Opinion Dynamics poll rating.

"Legal immigration is one of the top concerns of the American people and Congress's failure to act on it is a disappointment. The American people understand the status quo is unacceptable when it comes to our immigration laws. A lot of us worked hard to see if we couldn't find a common ground — it didn't work," he said.

But Senate leaders began to see the writing on the wall as tallies for the necessary 60 votes showed critical support had been lost. Part of the change of heart was no doubt spurred by public opposition, spurred by talk radio hosts.

Opponents of the bill — Republican Sens. Jeff Sessions of Alabama, who had been a frequent guest on the radio circuit, and Jim DeMint of South Carolina — remarked on the Senate floor that the sergeant-at-arms' office told them that the volume of calls leading up to the immigration vote was so high it had crashed the phone system, and no one was able to get through during morning debate.

Along with the senators' effort to slow the debate, the phone calls that came in "did make a difference," DeMint said after the vote.

Domenici, who once supported the bill and is up for re-election in 2008, told FOX News that Republicans are "getting hammered here at home and for what? Something that doesn't even have the chance of becoming law? No. This bill is going down. ... Why are we having all these big amendments? They (supporters) don't even know what's in this bill. We learned it's not even enforceable. I just don't think I can support this bill."

Many lawmakers who changed their mind and voted against the bill added that they didn't see the point of wasting their time when the bill was going to die in the House of Representatives. On Tuesday, only 23 of the 201 Republican congressman said they supported the bill. Internal Democratic counts were not made public.

Before the vote, members of the Congressional Hispanic Caucus cancled a morning meeting to lobby their colleagues in the upper chamber, and bill supporters in the Senate made one last, passionate pitch to keep the bill alive.

"This is a vote of enormous importance," Kennedy said. "This is really the vital vote about the future of the country or the past. Every person that votes 'no' has to know this situation is going to get worse and worse and worse."

Sen. Arlen Specter, R-Pa., called the bill "the very best that can be done."

"Let us finish this bill," implored Sen. Dianne Feinstein, D-Calif. "To cut this bill off now is a huge mistake. We are so close."

Prior to the vote, opponents appeared to sense that victory was within grasp. DeMint said the whole debate demonstrated why Americans are feeling a "crisis of confidence" in their government.

"This immigration bill has become a war between the American people and their government. ... This vote today is really not about immigration, it's about whether we're going to listen to the American people," he said.

"I don't pretend to know that I am on the right side or the wrong side of the American people," responded Sen. Lindsey Graham, R-S.C., a supporter of the bill who added that once the provisions are explained to Americans, polls show they overwhelmingly support it.

But Sen. Elizabeth H. Dole, R-N.C., said many Americans "don't have confidence" that U.S. borders, especially those with Mexico, will be significantly tightened, especially since legislation passed last year to set up hundreds of miles of border fencing had not yet been enforced.

"It's not just promises but proof that the American people want," Dole said.

Afterward, Sen. David Vitter, R-La., suggested that the Senate would be willing to consider "a supplemental appropriations bill to do the significant increased enforcement that we can clearly do."

Vitter added that their vote does not mean they are anti-immigrant, and to suggest that the 80 percent of Americans who opposed the bill are racist "I think itself is the height of ugliness and arrogance."

FOX News' Major Garrett, Trish Turner and Mike Majchrowitz and The Associated Press contributed to this report.