D emocracy, many people have said, is a matter of faith, but why, dear Lord, must our faith be tested so often? Lately, the role of money in political campaigns has been mocking our civic creed. "Here the people rule," we are taught, and we would like to think so. But if the voters (and nonvoters) seem disbelieving, they may merely be acquainted with the material facts of political life. Congressional candidates in this last election cycle raised $1.3 billion, which is a lot of money to change hands with pure intentions. Fiorello La Guardia, New York's reform mayor of the 1930s and '40s, once said that politics requires "supreme ingratitude." That's just the problem. Among those who run for office, ingratitude may not be common enough. In many respects, the United States is positively fastidious about the influence of money on public officials. Federal employees cannot legally accept even trivial gifts from the public. They risk prosecution if they allow someone to pay for a meal or...