[_delirium]

It's a good question; perhaps we can't. I think it's worth thinking about and considering if we really can't do anything to reduce likelihood or magnitude of corruption, though. The founding fathers spent a decent amount of time thinking about it in their own historical context, rather than leaving it purely to a trust that voters will punish politicians who behave badly. For example, the U.S. Constitution has written into it a prohibition on federal officeholders accepting titles of nobility, no matter how much voters like or dislike the politician in question; they just decided not to leave that question for the voters, but thought it would lead to less corruptible politics if politicians were completely banned from accepting noble titles. That at least doesn't seem to have had any particularly bad effects, though there is debate over whether it had good effects or was just symbolic anti-monarchism. It does seem vaguely analogous to some of the no-gifts clauses that have been proposed and/or implemented more recently, though the analogy isn't perfect.

[Gormo]

I think the founding fathers presumed that a certain level of corruption and abuse will always exist; their solution was to make it very difficult for any single political institution or office-holder to act autonomously, and deliberately constrained the exercise of power, so as to make effective corruption quite expensive and complicated.

Our modern trend toward increasing political centralization and removal of constraints on power is what's making corruption so lucrative and effective: if you build it, they will come.

Many of those who are most vigorously agitating for campaign finance reform want a strong and centralized federal government that isn't influenced by interests that compete with their own. But you can't have your cake and eat it too: if that's what you order, it's coming with a side of corruption (and a mixed metaphor fresh out of the blender).