The media and the people respond to who can present themselves as a "serious" candidate which, in other words, means that they have raised a ton of money. The problem is that to raise all that money politicians have to sell their soul to corporate, private, and social interests. They don't vote based on whats best for the country or for their constituents, they vote based on WHO LINED THEIR POCKETS.
If anyone thinks that their chosen political party is immune to this phenomenon then I'm afraid they have a lot more in common with the drooling brain dead masses than they would like to think. Money, money, money, money, money. That's what rules this country. It rules the media, it rules the political system, it rules everything. Right or wrong or good or bad or moral or evil has no place in mainstream politics in 21st century America.
The two most awesome examples of what our political system does to people are Mitt Romney and John McCain. Both respectable, reasonably principled, politicians who even I, as a Libertarian, respected on a lot of levels. The MOMENT that both of those guys decided to run for president they sold out everything they believed in, all common sense, all principles. They moved into step with the party (read: the money) and abandoned everything that they stood on principle for. In the United States you don't get to sit in The Big Chair unless you are just as corrupt as everyone else who sits in it.