In a landmark ruling that could affect state judicial elections nationwide, the U.S. Supreme Court on Monday said that due process can require a state judge to recuse when a party in a case before him or her has had a “significant or disproportionate” influence on placing the judge on the court through an outsized campaign donation.

The 5-4 decision in Caperton v. Massey Coal Co. introduces for the first time a constitutional standard into the debate over the influence of big money on judicial elections, which supporters said was a victory for the rule of law. Some reformers even expressed hope on Monday that the opinion would spur states to rethink judicial elections altogether and move to merit selection. But critics said the ruling sets a vague standard that will only trigger a flood of meritless recusal motions and sully the reputation of the judiciary, not enhance it.

Justice Anthony Kennedy, writing for the majority, said, “Due process requires an objective inquiry into whether the contributor’s influence on the election under all the circumstances “would offer a possible temptation to the average … judge to … lead him not to hold the balance, nice, clear and true.'” The “nice, clear and true” formulation comes from one of the few Court precedents on recusal, the 1927 case Tumey v. Ohio, which said judges must recuse if they have a direct financial interest in the outcome of a case.

Kennedy emphasized his ruling affects only extreme cases like the West Virginia case before him. In Caperton, Don Blankenship, chief executive officer of the Massey coal company, spent $3 million to help elect Brent Benjamin to the West Virginia Supreme Court of Appeals, while the appeal of a $50 million punitive damages award his company lost was on its way to that court. Benjamin was elected, refused repeated calls for him to recuse, and he cast the deciding vote in favor of his benefactor’s company. Author John Grisham has said he had the West Virginia case in mind when he wrote the 2008 thriller “The Appeal.”

All those factors — including the large size of the donation and the pendency of Blankenship’s company’s appeal while the election campaign was underway — made it “an extraordinary situation where the Constitution requires recusal,” Kennedy wrote. “The parties point to no other instance involving judicial campaign contributions that presents a potential for bias comparable to the circumstances in this case.” Kennedy also stressed that campaign contributions do not inherently create a probability of bias.

As a result, Kennedy said that even in the wake of the Caperton decision’s new constitutional line, “Most disputes over disqualification will be resolved without resort to the Constitution,” instead implicating only state laws and judicial codes of conduct.

But dissenters led by Chief Justice John Roberts Jr. were not so sure. They said the majority’s standard could lead to the filing of “Caperton motions” alleging judicial bias, “however groundless those charges may be.” Roberts added, “The end result will do far more to erode public confidence in judicial impartiality than an isolated failure to recuse in a particular case.”

Joined by justices Antonin Scalia, Clarence Thomas and Samuel Alito Jr., Roberts went on to list 40 questions the majority opinion does not answer about how the new standard will be applied. “How much money is too much money?” Roberts wrote. “How long does the probability of bias last?” He also wondered whether large contributions from an affected trade association or a racial or ethnic group, rather than an actual party in a case, would trigger the Caperton rule. And if a large contribution came from a lawyer, rather than a party, Roberts wrote, “must the judge recuse in every case involving that attorney?”

James Sample of the Brennan Center for Justice at New York University School of Law, who celebrated Monday’s ruling as “a narrow decision that is a huge victory for the rule of law,” nonetheless said that Roberts’ questions “are well-taken and will be addressed by state court judges” without resort to the Constitution except in very rare cases. “This was the ultimate scenario.”

American Bar Association president H. Thomas Wells Jr. applauded the ruling and announced that the association will develop “a series of guidelines for courts to assess whether contributions to judges’ campaigns implicate the due process rights of parties appearing before them. This evaluative process is one way to restore the public confidence in our courts so critical to preserving our government of laws.”

Former Colorado Supreme Court Justice Rebecca Kourlis of the University of Denver’s Institute for the Advancement of the American Legal System said she hopes the ruling will “create some momentum” for states to consider scrapping judicial elections and moving toward merit selection. “Election states may begin to think, ‘we can do better than this.'”

Theodore Olson of Gibson, Dunn & Crutcher, who argued in the case on behalf of the Harman Mining Corp. that won the damages award from Massey, could not be reached for comment. But David Fawcett of Buchanan Ingersoll & Rooney, who also represented Harman, said the decision was a welcome victory. “Everyone has a right to a fair trial and an unbiased judge under the Constitution. The idea that a corporate CEO could spend millions to influence the result in a case was a broadside attack on our system of justice. “

But Justice Antonin Scalia, writing a separate dissent, said not every wrong rises to a constitutional level. “The Court today continues its quixotic quest to right all wrongs and repair all imperfections through the Constitution.” Scalia said the Court was doing more harm than good by expanding “our constitutional mandate in a manner ungoverned by any discernible rule.”

Retiring Justice David Souter was part of the narrow majority, and the liberal Constitutional Accountability Center quoted from a 1996 speech in which Sonia Sotomayor, nominated to replace Souter, appeared to be in tune with the majority by criticizing judicial campaign contributions. “We would never condone private gifts to judges about to decide a case implicating the gift-givers’ interests,” Sotomayor said. But “our system of election financing permits extensive private, including corporate, financing of candidates’ campaigns, raising again and again the question what the difference is between contributions and bribes.”