A brief summary of congressional prostitution:
[…] As soon as individuals are elected to Congress, they start fundraising for the next campaign. They need to do this in order to win re-election. Fundraising is very grueling, and generally involves the representative grinding up to $15,000 per day out of friends, past donors, and lobbyists. There are even buildings around the U.S. Capitol set up precisely for members of Congress to call people and ask for money. Some spend 2-3 hours a day doing this.
One way to short-circuit the grueling phone-banking process is to call on lobbyists and ask them to throw a fundraiser for you. This involves a lobbyist setting up a breakfast, lunch, dinner, or cocktail outing and inviting a number of other lobbyists to show up, all of whom pay $500, or some other amount, to be there. The member of congress shows up, collects the checks, and the lobbyists get an audience with the member. These events happen all day every day.
Some members of Congress hold committee positions that make them particularly valuable for lobbyists, e.g. those on the Ways and Means Committee and the Financial Services Committee. Because lobbyists are more likely to lavish money on those members, the representatives who get those committee positions are expected to leverage those positions to raise money for their party as well as for themselves. Those who fail to raise a great deal of money in those valuable positions risk being replaced by party leaders.
So, members of Congress face fundraising pressures from political parties and from their re-election bids, and they often rely on lobbyists and donors to relieve those pressures. [… You] would have to be a fool to think that these donations do not affect voting decisions. On the majority of issues that the general public has no opinion about or knows nothing about, donations doubtlessly impact the way representatives vote.