Cypren says there are no more heroes running for political office who can keep their noses clean (along with Francis, in the comments), but I don't think such people have ever existed. In any social system -- democracy or depotism -- the people who rise to power tend to share similar characteristics. They have strong personalities, they're outgoing, clever, subtle, manipulative, and they have ambition. These are all powerful attributes and they will lead a person to great success, or to great failure. By their very nature such people will not tolerate any middle ground.
The people we see rise to power tend to be so endowed, and only come to our attention because they are great successes already. Sure, they may lose an election for president or governor, but they're already great successes by the standards of the world. The huge numbers of people with these qualities who never fall into the public eye are not middle-class professionals -- they're gamblers, criminals, con men, used car salesmen, and petty politicians (but I repeat myself).
So it shouldn't surprise anyone that every politician has a closet full of skeletons. Such people take risks, and suffer the consequences when they lose. It's hard to climb a mountain and never fall down; if you don't want to fall, you don't climb mountains. That's not to say that their failures are excused by virtue of their personality traits; we all have traits that incline us more towards certain failings than others, and we are all responsible for avoiding the temptations that accost us each individually.
One may also ask: why is it that most politicians are rich? Some are born into it, but again, is it really so surprising? Anyone who is a viable candidate for a major political office must have traits that would also allow them to be successful in that great American endeavor, making money. That's not to say they have business savvy -- there are plenty of other ways to make money. But I, for one, wouldn't elect a poor man to office. If you can't handle your own finances, stay away from mine.
So what does this mean? That character flaws are unavoidable and unimportant? Not at all. If a smart, ambitious, good person could be enticed into running for office, that would be excellent. But consider: every office requires someone smart, and no one who is unambitious will run... but what role does goodness play? There's so selection factor that encourages good people to run for office, and so they don't. Maybe there should be, but people just don't seem to care. Goodness is a bonus, and every other issue is non-negotiable.