He is alone with his thoughts, and his thoughts are dark ones. The film fools you on a first viewing. Is Travis an endearing eccentric? Sure, he's odd, but he's so polite, and he's got a quirky sense of humor. His affection for Betsy is actually rather endearing. But on a second view, you see it for what it is. The audience comes to see Travis's psychosis gradually, but there's actually far less development than one might think. When he talks about cleaning up the city, the repeat viewer knows he doesn't mean some sort of Giuliani-facelift. This is less a film about a character in development as it is a kind of snapshot. To be sure, it takes the stimulus to provoke the response, but does that imply some kind of central change in the character?
Tremendous supporting roles are brought to life through vivid performances by Keitel and Foster especially. Shepard's character, Betsy, is little more than a foil to highlight Travis's utter alienation from society, but she is still impeccably portrayed. With only two scenes that don't center on Travis, it is unavoidably De Niro's show. The life with which the supporting cast imbues their characters is a credit to themselves, and to the director's willingness to let the film develop from the intersection of diverse ideas and approaches. What would the plot lose by eliminating the Albert Brooks character (Tom)? Nothing at all. He makes almost no impact on Travis's life, which is where the plot lives. But his inclusion makes the film as a whole much richer and fuller.
As a piece of American cinema history, this film will live forever. But far more important than that, this film will survive as a universal, ever-relevant examination of the workings of the alienated mind. The story doesn't end when the credits roll. We know Travis will snap again. But the story doesn't end with Travis either. It continues today in the cities and in the schools. The film is about the brutal power of the disaffected mind.
This film didn't cause the incidents in Colombine, or Hawaii, or Seattle, or wherever you care to look, even with all of its disturbing images of violence. It didn't cause those things. It predicted them.