THAT the United States is a moralistic nation has, at times, been one of our greatest virtues and, at others, one of our vices. Americans have always debated politics with the moral fervor of the born-again, canonizing the politically upright and damning the unclean. The politics of the past two decades, with all its exaggerated emphasis on public wrong-doing, both foreign and domestic, is unusual in its intensity, though not in its nature.