They aren't really political parties per ce, but machines designed for no other purpose than to raise money. I recall in one of Bush's elections in the end the two platforms were less than 4% different, in Obama's last they were within 5%.
I have no idea how it happened, but the American electorate stopped caring somewhere along the line and figured second, no third best was just OK, "now gimme the ****ing tax cut". I believe the turning point came somewhere between "read my lips, no new taxes" and "I did not have sex with that woman".
You are correct, the electorate is guilty of being manipulated, look at how arguments in here NEVER end, whether it's Bush's record or Clinton, the memes continue in a never-ending cyclone of disagreement cum resentment cum hate. "Divide and conquer" has worked and Pogo was right "we have met the enemy and he is us!"
As earlier pointed out, they don't seem to suffer much, well paid, amazing perks, free lunches with lobbyists, who can blame them for exploiting a broken system to feather their own nest, while kicking all the cans down the road, generation after generation. I've never heard of a politician lose his job over illegals, nor over failing to bring in election reform legislation. Never since the Reagan and post-Watergate era, has the quality of government been an issue, seldom is the elected rock star held to account.
The sitting president was elected on "hope and change", remember that? There can't have been any change if this so called election is any indication.