For a gay leader who rose up in the 1970s out of the low-rent bohemia of San Francisco's Castro district, Harvey Milk came off as a fairly straight shooter. Running for the board of supervisors, Milk cultivated the look and demeanor of a mildly rebellious English professor.

Yet his squareness was more than a mask. It said: Here, at last, is a gay politician who's out of the closet yet knows how to work the system. What Milk's ebullient smile beamed to the world was how good it felt for an activist to lay his hands on power.

In "Milk," Gus Van Sant's incisive and stirring dramatization of Harvey Milk's heroic life and violent death, Sean Penn gives a brilliant and joyful performance, imitating Milk's Long Island Jewish whine and inhabiting his respectable suits with a nerd's awkwardness that's touching to behold.

When Milk stands before a crowd of demonstrators and waves his arms, out of some combination of wanting to inspire and not knowing where to put those arms when he speaks, he's a true man of the people: a noble schmo thrust into history because he realizes that if he doesn't lead, no one else will.

"Milk" is a fascinating movie – more docudrama than biopic because it immerses us in the political process. Much of the film is devoted to Milk's attempt to defeat Proposition 6, a statewide measure to ban gay teachers that he seizes on as a key issue of civil freedom.

With Anita Bryant as his foil of intolerance, Milk isn't just fighting for rights. He's leading a cultural crusade. It's creepy to see him forge a rickety alliance with Dan White, the conservative Catholic supervisor played by Josh Brolin as a dim politician and hooded soul.

As the study of a political moment, "Milk" is memorable. As a story of Milk's personal life, the film leaves out as much as it shows. That's a forgivable flaw, though, for the rare liberal message movie that lingers in the mind as well as the heart.