When I was growing up, people used to say that politics was the only game for adults. But I am persuaded, in my middle age, that they really meant it was rough, nasty, and largely devoid of rules. It cannot be much fun to run for office in the United States. And an election campaign, particularly for the highest office in the land, insults the intelligence of many voters. It features a level of vituperation we would not countenance on the playground of the most freewheeling kindergarten in the country.

The division and strife that characterize our political life, the substitution of slogan for argument and attack for policy, have grown so heated and painful that they threaten our pretensions to democracy. We face political discord that leaves us mired in mutual suspicion so deep that hardly anyone wants to talk to anybody with a different view. The challenge we face—especially we who are Christians—is what to do about it.

We know that God calls Christians to an ethic of love. He also forbids us to stay silent in the face of evil. How do we meld these competing mandates in our political stances? Over the years, I have heard and read answers that usually say a Christian is obliged to hold position X on issue Y. Sometimes this is surely true. But recognizing the causes for which we ought to fight is not the same as knowing how we should conduct the fight.

Thurgood Marshall, the longtime civil-rights lawyer and Supreme Court justice, who died 12 years ago this month, provides a model for how we should conduct ourselves. It was my great honor to serve as one of Marshall's law clerks, and, in his later years, to be a friend of the family. He was at all times a marvelous raconteur. One of his comments has long stuck in my ...