History is usually a tale of cruelty and folly, but it can also double back on itself in ways that move beyond irony to-ward something that can feel a little redemptive.

Standing in Chicago's Grant Park with the throngs last Tuesday night, I flashed back to when I was standing on Michigan Avenue just across from the park 40 years ago, an 11-year-old clutching my mother's hand as we escaped a bloody clash between police and demonstrators at the 1968 Democratic National Convention. I can still remember the smell of stink bombs and the sound of angry young people chanting, "The whole world is watching!" The Democratic Party's New Deal coalition ruptured right there. Now I've grown up and Chicago has grown up and the country has, too.

The 1960s have been much maligned and for some good reasons. The acrimony of the era spawned the red-blue polarization Barack Obama argued against in his 2004 convention speech and transcended in his presidential campaign.

But just as Obama is part of what he calls the "Joshua Generation"—standing on the shoulders of the civil-rights pioneers—he is the beneficiary of the spirit of the '60s among white baby boomers. The young people who came of age in the early part of that decade were inspired by the Kennedys and Martin Luther King Jr., who was stoned by angry whites in 1966 just for showing up in a Chicago neighborhood not far from where Obama lives now—a place where King, in the vernacular of the time, "didn't belong." These activists dreamed of a more just and peaceful world.

Then too many of them started acting stupid. The "yippies" in Grant Park in 1968 nominated a pig for president and hurled insults (and human feces) at police, who overreacted by mindlessly clubbing innocent people. The tumult of 1968 did more than inject a bitterness into American life that politicians like Richard Nixon could exploit; it soured a generation on politics. While some remained committed to social change, many more retreated into private and materialistic pursuits.

By the 1980s, these idealists were mostly on the sidelines as Chicago seethed with racial tension. In 1983 Democrat Harold Washington, an African-American, was nearly defeated for mayor by a Republican challenger whose slogan was BEFORE IT'S TOO LATE. This was the Chicago Obama saw when he arrived as a community organizer, distrusted at first by Chicago blacks.