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Campaign money also comes from people though, so if enough people care about an issue then even politicians who only care about raising money will respond. A quick google search shows that a large amount of Obama's money comes from individual donors (http://www.opensecrets.org/news/2011/10/grassroots-donors-sw...) so he has a strong incentive to do popular things.

Someone else posted that people who raise more money tend to win elections, but this could also be caused by the more popular candidate raising more money. People might also be more willing to send money to a candidate if they think that candidate will win since no one wants to waste money on a losing candidate.