It's not as outlandish or as hilarious as many of tales of Duke Cunningham's boffo corruption. But this article from Copley News Service describes what was likely one of the key necessary conditions of the Duke story: congressional 'earmarks', the practice which allows a member of Congress to stipulate that a given executive department fund a particular project or even give the business to a specific firm.
While the practice existed prior to the Republican takeover of Congress, the number of earmarks has more than tripled over the last decade of Republican control. And it's obvious why the ease of inserting earmarks is an open invitation to corruption.
The key is to understand the role earmarks have played in the political economy of the Republican majority. In anything remotely like fiscal policy, the GOP leadership has never been remotely conservative. The aim has been to harness the resources of the state to undergird Republican control -- in this case, by making more and more federal money available as patronage funds that leadership-compliant members of congress can use to reward donors and key constituencies. It's the Medicare Prescription Drug Bill fiasco writ small. And you can't understand the bigger story of what's happening to federal government today without appreciating this point.