In 1956 Adlai Stevenson, running against Dwight Eisenhower, tried to make the political style of his opponent’s vice president, a man by the name of Richard Nixon, an issue. The nation, he warned, was in danger of becoming “a land of slander and scare; the land of sly innuendo, the poison pen, the anonymous phone call and hustling, pushing, shoving; the land of smash and grab and anything to win. This is Nixonland.”

The quote comes from “Nixonland,” a soon-to-be-published political history of the years from 1964 to 1972 written by Rick Perlstein, the author of “Before the Storm.” As Mr. Perlstein shows, Stevenson warned in vain: during those years America did indeed become the land of slander and scare, of the politics of hatred.

And it still is. In fact, these days even the Democratic Party seems to be turning into Nixonland.

The bitterness of the fight for the Democratic nomination is, on the face of it, bizarre. Both candidates still standing are smart and appealing. Both have progressive agendas (although I believe that Hillary Clinton is more serious about achieving universal health care, and that Barack Obama has staked out positions that will undermine his own efforts). Both have broad support among the party’s grass roots and are favorably viewed by Democratic voters.

Supporters of each candidate should have no trouble rallying behind the other if he or she gets the nod.

Why, then, is there so much venom out there?

I won’t try for fake evenhandedness here: most of the venom I see is coming from supporters of Mr. Obama, who want their hero or nobody. I’m not the first to point out that the Obama campaign seems dangerously close to becoming a cult of personality. We’ve already had that from the Bush administration — remember Operation Flight Suit? We really don’t want to go there again....