WASHINGTON -- Lawyers hoping for a political appointment in the future, take note: the U.S. Senate is now judging attorneys based on their representation of politically unpopular clients.

In a move sure to rattle the legal community, a majority of senators voted Wednesday to block the confirmation of a respected civil rights lawyer to a top Justice Department spot because he helped get a convicted murderer off death row.

All Republicans and a handful of Democrats voted to sink Debo Adegbile’s nomination to lead the Justice Department's Civil Rights Division. The overriding reason for their opposition was that he once represented Mumia Abu-Jamal, a death row inmate convicted 30 years ago of killing a Philadelphia police officer.

Adegbile did not make the decision to take on the case. When he became the head of the NAACP Legal Defense and Education Fund in 2012, the group was already representing Abu-Jamal, and Adegbile continued to do so on a narrow constitutional issue. In other words, he was just doing his job by advocating for his client.

Many Republicans likely would have voted against Adegbile anyway. But several pointed to his past representation of the “Philadelphia cop-killer” as the reason for their opposition, and it was ultimately the votes of seven Democratic senators that did his nomination in.

"Why did we lose? Why did every single Republican vote against having lawyers defend people?," asked Sen. Patrick Leahy (D-Vt.), an ardent supporter of Adegbile, who currently serves as senior counsel to Leahy's Judiciary Committee.

Sen. Chris Coons (D-Del.), who is facing reelection this year and whose state sits within the Philadelphia media market, said he thought Adegbile was well-qualified for the position, but was concerned that he would face "visceral opposition from law enforcement on his first day on the job," citing the opposition to his nomination by several law enforcement organizations.

Along with Coons, the Democrats who voted against advancing Adegbile's nomination are Sens. Heidi Heitkamp (N.D.), Joe Manchin (W. Va.), Mark Pryor (Ark.), John Walsh (Mont.), Joe Donnelly (Ind.) and Bob Casey (Pa.).

Sherrilyn Ifill, who currently heads the NAACP Legal Defense and Education Fund, said Wednesday it was important to view the resistance to Adegbile within the broader context of opposition to the Civil Rights Division's work, pointing out that several nominees have had difficulty being confirmed.

"We understood that there was heavy emotional content here, but there was also a heavy principle here, and today the United States Senate really failed to advance the principle of rule of law," Ifill said on HuffPost Live Wednesday evening.

Attorney General Eric Holder, who would have been Adegbile's boss at DOJ, said senators had set a "very dangerous precedent" with the vote, which could allow for lawyers to "have their otherwise sterling qualifications denigrated based solely on the clients that their organizations represent.”

Ahead of the vote, members of the Bar of the Supreme Court warned senators against sinking Adegbile’s confirmation based on his representation of Abu-Jamal. In a January letter to Leahy and Sen. Chuck Grassley (R-Iowa), the ranking member of the Judiciary Committee, they argued that taking such action could send the wrong message to attorneys everywhere.

“LDF’s advocacy on behalf of Mr. Abu-Jamal does not disqualify Mr. Adegbile from leading the Civil Rights Division,” reads the letter. “To conclude otherwise would send the wrong message to any lawyer who is affiliated, or might be asked to become involved, with a difficult, unpopular case for the purpose of enforcing and preserving important constitutional principles.”

It’s not as if there aren’t other prominent figures in government who have had unpopular clients in the past. Representing a murderer in court didn't derail the confirmation of Chief Justice John Roberts to the Supreme Court. Roberts once devoted 25 pro bono hours to the case of John Errol Ferguson, who killed eight people and was one of the worst mass murderers in Florida's history.

Wade Henderson, who heads the Leadership Conference on Civil and Human Rights, said the vote on Adegbile revealed a "hypocritical" double standard.

"During the course of their long careers, both John Roberts and Debo Adegbile each performed a vital constitutional service by representing an unpopular client on death row," Henderson said. "Roberts is now Chief Justice of the Supreme Court, but opponents of the Adegbile nomination twisted reality and resorted to some of the dirtiest attacks I’ve seen in my professional career. Instead of extolling his admirable record of service, as the American Bar Association did, extremists turned this family man into a ‘cop-killer defender’ and a buffoonish racialized caricature."

A piece by a New York Times editorial board writer published Wednesday made a similar point. "Some have called Mr. Adegbile a 'cop-killer advocate,'" it read. "Another word for that might be 'lawyer.'"

Perhaps the most famous example of a lawyer tasked with representing an unpopular client is John Adams, who in 1770 represented the British soldiers charged in the Boston Massacre. His defense of the enemy didn’t stop him from getting elected to the colonial legislature that year, and from eventually going on to become president of the United States.

But things are different in the case of Adegbile. Even some of the Republicans who voted to block him on Wednesday have previously argued that it was important to separate a nominee’s views from the views that he or she may have expressed in court.

In Oct. 1990, Sen. Orrin Hatch (R-Utah) passionately defended then-Supreme Court nominee David Souter, who faced criticism during his confirmation process for defending literacy tests in his home state of New Hampshire. Hatch noted that those tests were existing law at the time, and that Souter, as the state's assistant attorney general, was required to defend them.

“It is not right to go back in hindsight and say he should not have done that; that that shows something wrong with him. Come on, that is what advocates do,” Hatch said at the time.

“If we are going to start using a nominee's briefs against him in the confirmation process, we are going to be setting a shocking precedent,” he continued. “It would be a very, very dangerous message to send to lawyers: If you have any ambition to be a judge, you lawyers, do not represent controversial clients and be careful what you say on behalf of a client because you might be held responsible for the fact that the law was as it was at the time you made the statement.”