Politics in general is a self fulfilling prophesy. Genuine, honest people who stand for something and want to make a positive change through integrity and compromise do not typically last long in politics. Those who are ruthless have the advantage and those who are not either need to recognize, defy and outnumber the ruthless, or else fall to their level, or fail to see the change they're fighting for. The job just incentivizes being a lying asshole.

Also that almost every election is a choice between a crook who'll implement the policies you want, and a crook who won't.