William L. Benoit described the problem very well:

The major problem in campaign financing is the fear that some donors expect their contributions to be rewarded with political favors, votes or decisions that candidates would not have made absent those donations. We worry that our elected officials are for sale to the highest donor.

Of course, donors protest that they aren't asking for favors. They only want to support candidates who share their priorities. Thus far, we have tried to solve this problem with limits on the donations. However, exploitation of many loopholes -- soft-money donations, to name one -- renders this solution unsatisfactory. (Insight on the News, Dec 11, 2000)