The focus of most of these comments has been on the film's perceived political commentary on American politics.
Let's make one thing clear: This film is a satire, not a commentary; in my opinion it's not about Republicans or Democrats, or conservatives or liberals; it is about the nature of democracies.
The point that the film, "Bob Roberts", makes can be summed up very clearly. Here is the nature of democracies: Voters choose winners over losers, champions over whiners, statements of power over statements of sacrifice. The list goes on; people prefer form over function, youth over age, presentation/entertainment over substance.
This film does transcend political lines; but in it's context, lets take a look at the specifics. Bob Roberts is electable because his message is just vague and occluded enough by his presentation, that he seems likeable. His message is not unique or original; he speaks to the elements that have always appealed to the more right-wing or fascistic elements of society; marginalization of the weak (in this case, the poor), empowerment of the common man, family values, etc.
Roberts' opponent, Paiste, is a textbook liberal; but this contest is not about left vs. right. Paiste is an educated man, and a career politician. He acknowledges the challenges in the American economy. He actually has answers to the issues; whether they are politically favorable or not is not significant. Roberts, on the other hand, says nothing about the real issues; he appeals only to the emotions of the mob, and because he uses the medium of folk music, he offends the sensibilities of liberals (both in the movie, and in its audience), because he uses the authenticity of the 60's and its messages of change, and "perverts" them to express his messages of reactionism and exclusion.
And it works.
Tim Robbins has a winner here, and this film gets overlooked because it gets dragged into these conversations about Robbins' own political views, and whether the film is making a statement about Republicans or Democrats. But Robbins says something far more universal with this film; democracies are not safe from tyranny or fascism; all it takes is a charismatic reactionary who can manipulate the interests of the press and the political interests to rise to power by appealing to the worst elements of our psyche, for entertainment, glamour, and exclusionism. Please remember that Hitler came to power by appealing to the worst aspects of the people of his nation, and was quite successful in creating much evil from that. Being part of a free nation comes with a huge responsibility; to carefully consider who we elect and what we value, and to allow those debates to have meaning. "Bob Roberts" shows us how easily we can neglect that responsibility, and how easily voters can be sold an offensive, exclusionary message, when it is wrapped up in something more attractive than what's real.
