A POPULAR conceit of the left is that political hatred is a sickness of the right, one to which liberals are largely immune. "Just who are these Clinton haters," asked Time magazine in April 1994, "and why do they loathe Bill and Hillary with such passion?" It answered, in effect: That's just the way conservatives are. The article quoted historian Alan Brinkley: "Liberals tend to value tolerance highly, so there's a greater reluctance to destroy enemies than among the right." That was a whopper even in 1994, a year when Republican leader Newt Gingrich was routinely vilified as a McCarthyite...