This is an amazing website that tracks campaign finance for political candidates. You will be able to see how much money is generated by the candidates, who donates and how much, which group and/or business has the most influence through their contributions. Pay attention especially to the section titled "Dark Money". Very interesting, indeed!
Open Secrets is sponsored by a nonpartisan, independent and nonprofit organization, the Center for Responsive Politics. They are the nation's premier research group tracking money in U.S. politics and its effect on elections and public policy. Their vision is for Americans to be empowered by access to clear and unbiased information about money’s role in politics and policy and to use that knowledge to strengthen our democracy. Their mission is to produce and disseminate peerless data and analysis on money in politics to inform and engage Americans, champion transparency, and expose disproportionate or undue influence on public policy.