Whats One of the highlights of the Politics on Film festival in D.C. this weekend will be the docu version of Thomas Frank’s book,“What’s the Matter with Kansas?”

The premise of the best-selling tome, published in 2004, is that the GOP was extraordinarily effective in building its base with working- and middle- class folks in the heartland who voted Republican even when it was not in their own economic self interest. In other words, social issues trumped class.

The documentary, from director Joe Winston and producer Laura Cohen, tests the limits of the thesis: That would be the 2006 election, when Republicans lost Congress and, as is seen in the movie, lost an attorney general’s seat in the state. The fractures are evident in the coalition that produced such a lopsided victory for George W. Bush in Kansas in 200. There’s a farmer who dropped out of the Republican party as he grew dismayed by the precarious nature of his way of life and the loss of community. As he notes, in the past when a farmer was in trouble, neighbors would rush to help. Now they wait for him to fail so they can buy land at bargain rates. Even some of the Christian evangelicals who are profiled, among the most stalwart of Bush’s backers, nevertheless acknowledge the failure of the Bush administration to plan for the occupation of Iraq.

And while the evangelicals remain a significant part of the base — John McCain also won the state by a smaller but still lopsided margin — the movie foreshadows the disarray to come with the economic collapse. When an outspoken pastor loses his ministry, in part because church elders find his anti-gay marriage and pro-life stances too controversial, he takes part of his flock to a new venue at a burgeoning theme park called Wild West World. But in something akin to the PTL scandal of the 1980s, a host of faithful investors lose hundreds of thousands when the amusement park goes under, and are left wondering why God led them down this path to a Ponzi scheme.

What makes “What’s the Matter with Kansas?” work, however, is not its colorful cast of characters and situations but its complexity. Other documentarians have approached the denizens of the heartland as if on safari. In “Kansas,” the filmmakers spend enough time with those profiled to get a sense of what led them to where they are. You may wring your hands as you listen to a suburban mom’s co-opting of the Christian label for fundamentalist beliefs, but there’s little doubt that her life improved when she sought salvation at a megachurch, an outlet not just for her faith but a singing career marked by gigs at a Wichita Best Western.

The film exposes the basic ironies that Frank does in his book, and it also points to what went wrong with Democratic liberalism in the 1980s and 90s. Frank says that the Democrats lost touch with the rank-and-file, the populist class that generations ago made Kansas a hotbed of socialism and radicalism. A case in point is the Democratic support of NAFTA, leaving union die-hards disaffected and, by default, flocking to Republicans and their traditional family values. (Among those caught in the cross hairs is Dan Glickman, who voted for the trade agreement and lost his seat in 1994.)

The economy once again trumps cultural politics, perhaps a primary reason for the current Republican disarray. But as “Kansas” suggests, it doesn’t mean that the populist tradition of the state is about to swing left again. It’s still up for grabs.