When Chicago’s 1968 Democratic National Convention erupted in violence over the war in Vietnam, Bill Siegel–then six–watched the news on television at a cabin in northern Minnesota as his family argued around him. His aunt, a delegate for Eugene McCarthy, eventually stormed out the door and drove to Chicago, and Siegel says he still remembers his mother’s disgust when candidate Hubert Humphrey drew the curtains of his Hilton suite on the mayhem below. The next morning Siegel’s dad–a World War II veteran and at the time “a classic Minnesota Humphrey liberal”–yanked their flagpole out of the ground and tossed it into the woods.

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Siegel, who now lives in Rogers Park, and San Francisco filmmaker Sam Green revisit many other divisive episodes from the decade or so that followed in their new documentary, The Weather Underground, a portrait of the militant leftists who split off from the nonviolent Students for a Democratic Society in 1969. The film, four years in the making, focuses on the era during which the Weathermen–at their peak, perhaps 300 members strong–bombed the Capitol and the Pentagon, sprang Timothy Leary from jail, and lost three of their own when a pipe bomb accidentally went off in their Greenwich Village town house, an event that drove the remaining members deep underground.

A handful of Weathermen (all with their backs to the camera) participated in Emile d’Antonio’s 1976 documentary Underground because, says Bernardine Dorhn–who’s gone from the FBI’s Ten Most Wanted list to teaching law at Northwestern–“we could speak to a lot of people.” But for some–including Dohrn and her husband, Bill Ayers, now a professor of education at UIC–The Weather Underground is the first documentary in which they’ve spoken openly about their decade underground. Dohrn and Ayers come across as doctrinaire as ever, but Siegel and Green’s impassioned film is open-minded about the radicals’ critique of American imperialism, racism, and capitalism, refusing to present their beliefs as propaganda in amber. Unlike the teach-ins that characterized the early days of SDS, the Weathermen’s tactics–bombs and strident, unsigned communiques–did not invite dialogue. But as depicted by Siegel and Green, the group’s worldview emerges as a history lesson far more nuanced than its original hard-line dogma. “It’s a film for the whole family,” says Siegel, noting that, post-September 11, younger generations will look at the Weather Underground’s attacks on government property differently than the group’s peers did.