It used to be that if a person in Congress hoped for a position such as a committee chair, he or she got it mainly through seniority and service. Within a couple of years, they started having to put money into the party coffers in order to get ahead, a topic studied mainly by Tom Ferguson. That just drove the whole system even deeper into the pockets of the corporate sector (increasingly the financial sector).
This cycle resulted in a tremendous concentration of wealth, mainly in the top tenth of one percent of the population. Meanwhile, it opened a period of stagnation or even decline for the majority of the population. People got by, but by artificial means such as longer working hours, high rates of borrowing and debt, and reliance on asset inflation like the recent housing bubble. Pretty soon those working hours were much higher in the United States than in other industrial countries like Japan and various places in Europe. So there was a period of stagnation and decline for the majority alongside a period of sharp concentration of wealth. The political system began to dissolve.