Washington ? Here come the Sixties again, hijacking another presidential campaign with their endless generational pathologies.

This time it’s John McCain, Vietnam vet, trashing Woodstock and Hillary Clinton, a woman some view as the high priestess of the baby boomer left.

You may have missed it, if you’re not a navel-gazing boomer (“Hey! Woodstock was really important! Because we were THERE, man! In the MUD!”) or an old Establishment square still disdainful of your once-long-haired younger cousins.

McCain scored points at a recent Republican presidential debate by criticizing a $1 million federal earmark request from Clinton and Chuck Schumer, fellow boomer-New York Democratic senators, for a museum to commemorate the 1969 Woodstock concert, a cultural touchstone for the boomer generation.

Said McCain: “Now my friends, I wasn’t there. I’m sure it was a cultural and pharmaceutical event. I was tied up at the time.”

Big laughs and cheers. That last bit was a reference to the fact that McCain languished in a North Vietnamese prison as The Who celebrated “My Generation” for about 500,000 stoned rock fans whose chief deprivation was a port-a-potty shortage.

McCain’s line went over so well that he turned it into two television ads, complete with a dancing hippie chick and psychedelic colors.

The ads highlight his anti-spending crusade, but they’re more significant in that they draw squarely from a tried-and-true politico-cultural playbook: Raise middle America’s qualms about Democrats generally and the Clintons specifically by painting them as barely reconstructed, untrustworthy hippie-lefties. Certainly, Bill and Hillary looked the part back in the day, all that hair and denim. (Although it appears that neither went to Woodstock.)

So once more, American political discourse is hostage to the cultural psychodrama of the 1960s.

It happened in 1992, when Bill Clinton, the first boomer to run successfully for president, was criticized for protesting the Vietnam War, evading the draft and even – GASP! – traveling to the Soviet Union as a young man.

It happened, though less virulently, in 2000, when allies of George W. Bush and Al Gore traded barbs about whose military service was more significant and whether either received help in getting his berth.

The 2004 election was like living the era all over again, with John Kerry’s Vietnam record questioned and his antiwar activities savaged, while Bush’s record in the Texas Air National Guard got yet another scrubbing.

“The reason the Sixties keep rearing its head is it’s not over,” said Roger Kimball, a cultural critic who wrote “The Long March: How the Cultural Revolution of the 1960s Changed America.” “The ’60s didn’t end when the last electric guitar was unplugged at Woodstock.”

Those who were on opposing sides of the cultural fault line that opened in the ’60s continue to fight over what it all meant and what it continues to mean to our society, Kimball said.

So the ’60s-centric attacks probably will continue as long as the boomers dominate our politics. That’s one of the rationales behind Barack Obama’s candidacy. Though his 1961 birthday technically makes him a boomer, his experience is wholly distinct from the generational squabbling of those who came of age in that decade. He was, after all, 8 years old when the hordes converged on Max Yasgur’s upstate New York dairy farm.

Maybe Obama could get an earmark for a Michael Jackson museum.