A real argument starter, this documentary by Henriette Mantel and Steven Skrovan considers the life and legacy of Ralph Nader, the tireless public-interest advocate who alienated many of his natural allies when he ran for president in 2000 and 2004. Though filled with talking heads and clocking in at two full hours, it’s thoroughly involving, and its two-part structure explicitly balances Nader’s phenomenal career as an anticorporate gadfly in the 60s and 70s with his role in the election of George W. Bush. Pissed-off liberals Todd Gitlin and Eric Alterman denounce Nader as a megalomaniac and traitor to his own cause; longtime friends and associates describe him as reluctant to run for office, driven only by conscience and frustration with the Democratic Party’s sellout to corporate interests. Through it all Nader comments on his adventures, as ruefully funny as ever. 122 min.