but don't forget the special interest groups... those are also getting voted on. If they are backing a candidate and the candidate wins, they want to get 'paid' for it with political favors.
the American Democratic systems comes down the Business Party (Republicans) vs. the Workers Party (Democrats). The most basic defination of each party is; What is good for business is good for the nation, and What is good for the workers is good for the nation. Like most things that do not live in a vacuum, the reality is somewhere in the middle.
The special interest groups are worse than that though, as they focus on their tiny little agenda with whichever party is likey to promote their agenda. So Kerry got the Pro-choice group, and Bush got the evangelical christians and the Pro-lifers... Problem is, there are dozens of theses groups pushing their agendas and they expect to be paid if their candidate wins. Things aren't that simple today, especially with the war/terrorism going on.
People need(ed) to approve a candidate that espouses a platform beyond their typical tiny focus group and most people are ignorant of the 'bigger picture'... or perhaps not since Bush won 
I still believe a 3rd major party would spread around these groups, so people could vote FOR a candidate that more closely matches their beliefs, rather than AGAINST the candidate that doesn't
