Opponents of President Obama's nominee to head the Justice Department's Civil Rights Division prevailed in blocking his confirmation Wednesday, as he failed to clear a procedural hurdle.

Several Senate Democrats joined with Republicans in voting against Debo Adegbile, whose nomination was adamantly and vocally opposed by conservatives due to his participation in an appeal filed on behalf of Mumia Abu-Jamal -- an internationally-known prisoner convicted of the 1981 murder of Philadelphia police officer Daniel Faulkner.

The vote was expected to be close -- with Vice President Biden on hand to potentially cast a tie-breaking vote -- but the final tally was 47-52 in opposition to the appointment.

In total, eight Democrats voted against confirmation in the final tally. Initially, seven Democrats voted against confirmation and Majority Leader Harry M. Reid (D-Nev.) -- who initially voted in favor of confirmation -- later switched his vote to no, giving him the right as Senate leader to bring up the nomination again at a later date.

Adegbile becomes the first Obama nominee rejected under the new Senate procedures approved in November that require just a majority of senators present to agree to proceed to a vote on most presidential nominees.

In a statement released following the vote, Obama blasted the senators who voted against Adegbile's nomination, saying they "denied the American people an outstanding public servant."

"The Senate's failure to confirm Debo Adegbile to head the Civil Rights Division at the Department of Justice is a travesty based on wildly unfair character attacks against a good and qualified public servant," Obama said, later adding: "As a lawyer, Mr. Adegbile has played by the rules. And now, Washington politics have used the rules against him."

Other Democrats who voted against the Obama nominee were Chris Coons (Del.),Bob Casey (Pa.), Mark Pryor (Ark.), Heidi Heitkamp (N.D.), Joe Manchin (W.V.), Joe Donnolly (Ind.) and John Walsh (Mont.).

“I made a conscientious decision after talking to the wife of the victim,” Manchin told reporters. But the senator, who usually likes engaging with reporters, was otherwise tight-lipped on his decision, saying repeatedly that “I made a conscientious decision.”

The decision by seven Democrats to buck their party leadership and the White House caused a rare split in the Democratic caucus, which usually votes in lockstep on Obama’s nominees. A senior aide to one of the senators who voted against the pick said several offices were “very angry” with the White House for moving ahead with the Adegbile nomination even though they knew it created an unnecessarily uncomfortable and politically treacherous vote for several vulnerable Democrats in tough reelection races this year.

"It's a vote you didn't have to take. It's a 30-second ad that writes itself,” said the aide, who asked for anonymity in order to speak frankly.

Adegbile, 47, spent more than a decade working for the NAACP Legal Defense Fund, where he served as the group’s in-house voting rights expert. The legal defense fund began its work on Abu-Jamal's behalf well before Adegbile began working for it, however he did contribute to the filing of a 2009 court brief that argued that Abu-Jamal faced a discriminatory jury -- an appeal later found to have merit by a judge.

But, that participation in Abu-Jamal's appeals, opponents including Faulkner's widow have argued, should disqualify him from holding any publicly appointed position in the justice system.

Several prominent Republicans, including Senate Minority Leader Mitch McConnell (R-Ky.), took the floor Wednesday to speak in opposition to the nomination and in hopes of swaying vulnerable Democrats facing re-election in red states.

Prominent Democrats -- including members of the Congressional Black Caucus -- have defended Adegbile's nomination and resume, arguing that his lengthy history of work on voting rights issues made him supremely qualified for the post.

In the final speech before the vote, Reid called the GOP opposition to Adegbile "an affront to what it means to live in America," and -- noting Adegbile's history with working on voting rights cases -- said it is part of a larger Republican strategy to disenfranchise minority and impoverished voters.

"They want fewer voting people. They don't want people to vote and they especially don't want poor people to vote." Reid said.

But in the end, it was the votes of Democrats -- not those of Republicans -- that doomed Adegbile's nomination.

"At a time when the Civil Rights Division urgently needs better relations with the law enforcement community, I was troubled by the idea of voting for an Assistant Attorney General for Civil Rights who would face such visceral opposition from law enforcement on his first day on the job," Coons said, in a statement released after the vote. "The vote I cast today was one of the most difficult I have taken since joining the Senate, but I believe it to be right for the people I represent."

“The vote I cast today was one of the most difficult I have taken since joining the Senate, but I believe it to be right for the people I represent.