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.