How was "The Dark Knight" political?

It's basically the theme of the entire movie. I suck at explaining these types of things, but I'm going to try. The last couple minutes of the movie pretty much explains it. Politicians are what people need them to be. Batman ends up taking the fall for the things Harvey did, and his exact words were something like "Gotham needs a real hero." Well, that wasn't exact, but it was close enough. We put so much trust into the people who govern us, and it's a huge disappointment when they screw up. I don't really see how it relates specifically to today's politics, but I see how it relates to politics, in general. I'm sorry if that didn't help at all. I can understand things, but I don't do well at getting it out.