Who -- me, biased? For a lousy $3 million?

In a closely watched case that illuminates a common (and powerful) bias in human decision-making, the U.S. Supreme Court ruled today that the Constitution can require a state court judge to step aside when he is faced with a case involving a major campaign donor.

The case involves Brent D. Benjamin, now the chief justice of West Virginia's Supreme Court, and the Massey Energy Co., his major campaign contributor.

West Virginia, like most states, allows judges to be elected (instead of being appointed). And Massey's chairman, Don Blankenship, had spent $3 million in the 2004 election attacking an incumbent for the court. The incumbent lost and Benjamin won, which turned out to be a good thing for Massey: Benjamin twice joined 3-2 majorities to throw out a $50 million verdict against Massey, which was involved in a long-running dispute with another coal company.

Writing for the majority of the U.S. Supreme Court, Justice Anthony M. Kennedy noted that no “quid pro quo”had been established between Mr. Blankenship’s campaign contributions (which dwarfed those of other donors in the judicial elections), and Justice Benjamin’s stance in the lawsuit. But there was, he noted, “a serious, objective risk of actual bias.”

This squares with a raft of recent research on bias and gift-giving. As we've pointed out before, even a small gift like a coffee mug can bias the judgment of the person who receives it. The same is obviously true for a $3 million campaign contribution. No explicit quid-pro-quos are necessary; that's because the bias is implicit -- and inherent.

In fact, when judging the conduct of others it can be incredibly hard to be impartial -- even when we are trained to be unbiased. For an illustration of just how hard, see Justin Wolfers's eye-opening look (with Joseph Price) at biased officiating by NBA referees.