In an election year, candidates are holding forth predictably about finding solutions to persistent problems, fixing ineffective programs and even—at last—meeting the needs of the American people. William G. Howell and Terry M. Moe, professors at the University of Chicago and Stanford University, respectively, think that a change in the very structure of American government is needed before any such promises can be kept. The thesis of “Relic” is that the United States is “burdened with a government designed for a bygone era.” The times have changed, “but the core of the Constitution . . . has not.”

The...