Indeed; people and organizations just contribute to the campaigns of people who already happen to support the policies that benefit them. Sometimes there's a sense of reciprocity, and sometimes there's small-scale corruption (e.g. Corporation X donates money to the campaign of Mr. Congressman, who in turn votes for an appropriations bill where the Pentagon orders 10 million units from Corporation X), but it doesn't seem to influence individual opinions on broad-scale policy. It's not as often that people get elected on an animal rights platform and then start taking money from Big Fur and turn around and vote for clubbing baby seals or something like that. Big Fur just saves their money and donates to the pro-seal-clubbing candidate in the first place.