Victor Davis Hanson writes on "The Crazed Fringe":

When I was growing in rural California in the 1950s and 1960s, my FDR parents winced at the nut right-wing fringe. This was, remember, the era of bulk mailings on pink paper, crazy “Did you know?” unsolicited newsletters detailing the names of local and national communists, usually sent from strange addresses in the Sierra Nevada foothills. At seven and eight, we used to pick them up from the garbage and ask our parents, “Hey, Mom, are Lucy and Ricky really communists?”

My cattleman uncle Tango used to stop by with John Birch literature, warning us about the impending fluoride conspiracy to make us all impotent.

The boy-scout troop leader would stop by, trying to sell us his version of a metal bomb shelter (a septic tank with hatches), and preached how we could win a nuclear war against Castro et al.

A neighbor used to preach to us that Caesar Chavez was employed by the KGB, and that the UFW was controlled by Moscow. The local paper’s op-eds still fought over Social Security and the Minimum Wage as equivalent to the Revolution of 1917. And always were the “hate the Jews” subtexts and allusions, alleging some sort of world banking conspiracy to rob us white rural folk who worked hard to send our peaches eastward only to have them hijacked and resold at ten times what they gave us by long-nosed crooks “on the East Coast”. You get the picture—the Right had a problem with its so-called wing nuts.

But over the years, conservatism came to terms with civil rights and anti-Semitism. Free markets, not socialism, enriched America and brought a level of affluence undreamed of it to the poor. (When I was seven, outhouses and unpaved roads were common in West Selma; today in the same neighborhood you see SUVS, new tract houses, and I-pods and blue teeth in the ears of illegal aliens.). And so the Klan, Birchers, and other assorted embarrassments were peeled off.

The left in the 1940s and 1950s had likewise gotten rid of its communist wing, and ostracized its fellow travelers. Henry Wallace was taken off the ticket. Dean Acheson and George Kennan had made liberal anti-communism logical rather than paradoxical.

But now the Left, still going on the fumes of the 1960s, has the greater problem with its extremists. Of course, the “base” can attack Bush on immigration, gay marriage, etc. but not from a position of sheer lunacy. The same is not true of the netroots or the Cindy Sheehan/Michael Moore wing on the Left. They openly praise our enemies, whether in Syria or Iraq (“Minutemen”). They prefer the unfree world of Chavez and Castro to our own. And their language and methodology are as uncouth and repulsive as were the old tactics of the Birch Society.

A possible cause for that shift is explored in James Piereson's new book Camelot and the Cultural Revolution. He argues rather convincingly that it began to occur when mid-sixties liberals were unable to culturally process the ideology of the man who shot Kennedy. But whatever the reason why, a remarkable shift has seemed to happen over time, as VDH notes.