America has a political generation gap again, right on schedule. The baby boomers' kids — now nearly all of voting age and more numerous than the generation that spawned them — are flexing their political muscle in a way that puzzles many of their elders.

The gap was on vivid display in Iowa's Democratic caucuses last Monday. A Washington Post entrance poll (the precinct caucus equivalent of exit polls) found Hillary Clinton besting Bernie Sanders by 23 percentage points among caucusgoers between ages 45 and 64 and by 43 percent among those past age 65. Among those between ages 17 and 29, Sanders enjoyed a whopping 70 percentage point advantage.

To put a Minnesota frame on it, one might say it's Eugene McCarthy vs. Hubert Humphrey all over again. And for Democrats, that's not exactly a comforting analogy for those who know how that generational tug of war turned out. The 1968 clash of two of Minnesota's own helped elect Republican Richard Nixon.

Yet Sanders' campaign seems to be inviting comparisons to 1968 — or so I thought as I watched Sanders' video ad with the evocative Simon and Garfunkel 1968 song "America" as its soundtrack. Viewers who did not live through that wrenching year may consider the song patriotic and even upbeat when paired with wholesome images of Iowa farm country and a Sanders campaign rally. Those who hummed that tune when it was new are more likely to hear its melancholy undertone. The full lyrics, which aren't used on the ad, are the lament of disillusioned youth seeking something lost — innocence, perhaps, after nation-changing bloodshed that year in Memphis, Los Angeles and Vietnam.

The 1968 election has been on my mind for another reason. I recently read Norman Sherman's new memoir, "From Nowhere to Somewhere: My Political Journey." Sherman is a native Minnesotan and a two-time Minneapolis Star and Tribune janitor (a noble calling!) who served Humphrey as press secretary both during his vice presidency and his 1968 presidential campaign.

As Sherman attests, a generation gap in American politics is a disruptive force. For Humphrey in 1968, Sherman wrote, it meant that "as he moved around the country, for every smile there was a frown, for every cheer, a louder jeer. Vietnam was a proximate, constant aggravation. … It overwhelmed anything good happening domestically."

Beginning in 1967, antiwar, pro-McCarthy protesters dogged Humphrey's every public appearance — a painful ordeal for a practitioner of "the politics of joy" whose private views on Vietnam policy were not as different from those of McCarthy as Lyndon Johnson's loyal-to-a-fault vice president let on. The mood of the country was ugly and grief-stricken after the assassinations of Martin Luther King Jr. and Robert Kennedy. Even at elite Stanford University, protesting students threw human excrement at Humphrey.

Nothing that brutal has marred the presidential race this year. Much has been made of the anger in the American electorate. But today's unhappiness has not reached the fever level caused by an unpopular war and a military draft that sent young Americans far from home to fight and, in 58,000 cases, to die. In the Minnesota vernacular, today's political mood "could be worse."

But Sherman counseled when I reached him at his Arizona home last week that the political potency of today's young voters ought not be discounted. Their thinking may have roots in their parents' youthful political ventures, he opined. "It should come as no surprise that the Vietnam generation has progeny who believe government ought to be cleaned up somehow," he said. Suspicion of the governing establishment could well be a heritable trait.

To that, I'd add that for some millennials, the Great Recession and its aftermath may provide political motivation as personal and compelling as war and the draft were a half-century ago. American boomers told their children in the 1980s and 1990s that they could grow up to do whatever they chose and earn a middle-class income to do it. When those children graduated into a mean economy carrying a heavy burden of college debt, many found their career options limited and middle-class comforts out of reach. As homeownership and parenthood were postponed, resentments have grown.

A sense of generational letdown could well explain millennials' support for a presidential candidate offering free college tuition, higher wages and Medicare for all. The fact that said candidate is an often-dour 74-year-old from Vermont who calls himself a socialist evidently doesn't repel them — any more than the "Clean for Gene" army was put off by the often dour and diffident poet-politician from Minnesota nearly 50 years ago.

Will parallels to 1968 persist in the Democratic race? They just might. One can imagine Sanders opting for an increasingly divisive campaign in coming weeks, employing rhetoric that makes Clinton increasingly unacceptable to Sanders' young supporters. One can imagine Clinton winning the Democratic nomination despite Sanders' negativity — or maybe with the help of the backlash that might follow a barrage against a groundbreaking female candidate. One can imagine an embittered Sanders finding himself unable to endorse Clinton or, if he can, unable to muster the sincerity to swing his supporters to her side.

Eugene McCarthy did not endorse Hubert Humphrey in 1968 until Oct. 13, two weeks after Humphrey belatedly broke with Johnson's Vietnam policy and announced that if elected, he would stop bombing North Vietnam. On Nov. 5, Nixon's winning margin in the popular vote was 0.7 percent.

"What if Gene McCarthy had found a generous and forgiving and appreciative heart in his body? He could have helped diffuse the anger and animosity that dogged us," Sherman wrote about Humphrey's defeat.

Alternatively: What if Bernie Sanders resists the temptation to drive the generational wedge deeper? What if he begins speaking to a wider demographic spectrum? What if Hillary Clinton makes a visible and persistent effort to respond to the legitimate concerns of her daughter's generational peers, even if it means breaking with the policies of Barack Obama and her own husband? They just might. They're both old enough to remember 1968.

Lori Sturdevant, an editorial writer and columnist, is at