The unsavory career of Jack Abramoff, the Washington lobbyist whose corrupting influence tainted the Republican-controlled Congress during the early years of the present decade, is recounted in meticulous—if not absolutely complete—detail by Alex Gibney (“Taxi to the Dark Side”) in his new documentary. It’s a morose but instructive story about the destructive influence of money—and fanaticism—on American government.

Gibney begins with a “grabber,” a re-enactment of a shooting in which, he suggests, Abramoff was involved. But that’s quickly abandoned to go back to his subject’s early years in the College Republicans, which he was instrumental, along with Ralph Reed and Grover Norquist, in transforming from a relatively moderate group into a hotbed of ultra-conservative activism. The capper comes in his efforts as a movie producer with a decidedly ideological agenda, most notably with “Red Scorpion,” a dismal Dolph Lundgren picture from 1989 that aimed to make a hero of an Angolan dictator.

The meat of the film, however, deals with Abramoff’s lobbying activities, the beginning of which coincided with the Republican takeover of 1994 and the ascendance of Newt Gingrich and Dick Armey. A good deal of time is devoted to his manipulation of Indian tribes that hired him to represent their interests, tribes that he fleeced mercilessly, and to his campaign to maintain the exemption of Saipan and the Mariana Islands from the stipulations of US labor laws, despite the abuses that entailed, in the name of unrestrained free-market economics. His close collaboration with Tom DeLay, the new House speaker, and with the Bush White House is also covered, as is his hiring of old buddy David Grosh, a slacker-style lifeguard, to “head” the so-called American International Center, a front for laundering his ill-gotten gains.

Of course Abramoff’s machinations eventually led to charges of conspiracy, bribery and fraud, and to the conviction not only of him but of numerous associates, including government officials and even members of Congress. The fallout helped insure the Democratic takeover of Congress in 2006.

This is an enormous amount of material to pack into two hours, even with the inevitable elisions and omissions, and Gibney’s sober but slanted coverage of the scandal can be fatiguing. But it’s an important story, and one that’s been largely forgotten in the wake of other crimes and misdemeanors. Certainly Gibney’s assembled a wealth of material not only from archival sources but in terms of new interviews with associates, critics and commentators (though not with Abramoff himself, who’s represented by congressional testimony and e-mails), and he and editor Allison Ellwood have stitched it together skillfully. In other technical respects, too, this is a class job, with Maryse Alberti’s cinematography first-rate and John McCullough’s score apt, even if at times the selection of pop tunes used to comment on the sordid goings-on is rather obvious.

“Casino Jack” teaches an important lesson about money and politics, and voters in this country would benefit from hearing it. That’s why it’s a pity that the people most likely to see it will be political junkies for whom its message will be old and familiar news. But in documenting so well one of the more egregious examples of the corruption within the Washington establishment, Gibney has does a real service; and since one of the main points about the Abramoff-DeLay agenda was its rabid push for deregulation, it’s an episode that retains its relevance in the current national debate. Unfortunately, the film is likely to be relegated to the special-interest ghetto that houses most activist documentaries that take on issues like the one covered here. That’s a pity, but it’s also the reality; and as long as Americans have such limited interest in the way their government is run and such short memories about scandals like this one, things aren’t likely to improve much.