By the time a drunken Dan White (Josh Brolin) greets — and confronts — fellow supervisor Harvey Milk (Sean Penn) outside Milk’s crowded birthday party in City Hall, the straight-laced former cop has already tipped unsuspecting audience members he’s tightly wound and has a single-minded focus that borders on explosive. That’s one reason the intense scene jars all the more: It graphically brings home the awareness that White is coming unglued and foreshadows what other viewers know before coming to the theater: that this is Milk’s eventual killer. In the space of that one riveting foyer moment, Brolin portrays White’s struggles with acceptance, possible sexuality confusion and other hidden demons, while Penn essays a suddenly unnerved Milk, hinting at the tragedy that even the flamboyant camera store owner suspects is in the offing.