On the eve of the conventions, watch the best movie ever made about the people living, working, and agitating on the margins of America's grandest political theater tradition. Set during and filmed amid the chaos of Chicago 1968, Haskell Wexler's film is a heady mix of protest chic, Appalachian romanticism, and agony over journalistic objectivity. The phrase "medium cool" refers to Marshall McLuhan's theory that TV is a "cool" medium—one that invites viewer participation—in contrast to the "hot" quality of film, which sucks up all your attention and energy. Medium Cool may be hot, but it wants you to holler back. (Northwest Film Forum, 1515 12th Ave, 267-5380. 7 and 9:15 pm, $8.50.)