Other than the reasons already pointed out, money plays a huge role in elections in the U.S.A. Without large influx of money, a politician can not run an effective campaign - hence corporations have a huge leverage. To put it bluntly: corruption is rife in the U.S. but it is "hidden" as money does not (always) go directly to a politician's pocket, but it is diverted to his/her campaign. What the U.S.A. needs is to revamp its law and limit contributions to small amounts per person - including corporate persons - and reverse the Citizens United ruling through a constitutional amendment.
Money in politics is certainly an issue, but I think it pales in comparison to our lack of proportional representation in Congress. Many communities are now distributed across the country, which can effectively deprive them of representation unless they have a critical mass in at least one place (I assume Silicon Valley is a good example).
