The compelling documentary "An Unreasonable Man" carries the tag line, "Ralph Nader: How do you define a legacy?" but it might just as easily have asked, "Who gets to define the legacy?"

With its two hours divided between exploring Nader's four-decade career as a consumer crusader and the fallout over his controversial 2000 presidential bid, the film portrays him as a revolutionary figure whose primary accomplishments have been overshadowed by politics.

Directors Henriette Mantel and Steve Skrovan interviewed Nader along with supporters, critics and pundits in compiling a thoughtful, appreciative assessment of Nader's work as an activist and the anger stirred by the impact his campaign had on the Al Gore-George W. Bush election outcome.

Whether you hold Nader accountable for Bush's victory, feel he was justly pursuing a noble cause or simply wish he would go away, there are bound to be segments of "An Unreasonable Man" that will rankle you.

The film's second half, which deals with the fact that Nader's recent political ambitions have largely overshadowed his work as a consumer advocate — notably in the field of auto safety — is telling in that some of the harshest rebukes come from onetime allies.

It's from "Nader's Raiders" alumni that we hear both the most praise and the most disappointment. Nader professes no interest in his legacy, satisfied that the existence of seat belts and air bags are evidence enough of what he accomplished. But Mantel (who once worked for Nader as an office manager) and Skrovan seem intent on getting him a fair hearing.

Though the second half contains the fireworks, it's the film's first hour that is ultimately most memorable. Mantel and Skrovan do a commendable job in covering a lot of territory, mixing pertinent and entertaining archival footage with interviews detailing Nader's rise to prominence and the uphill battle he faced following the "Reagan Revolution" in 1980.

The back and forth over Nader's impact on the election seems as unproductive now as it did seven years ago, but the chronicle of what Nader and a mobilized force of idealistic young people accomplished, primarily in the late 1960s and early 1970s, is impressive in its undeniable long-term effects.