The thing you've got to understand about America is that we've got two kinds of people.
Well, no, that's not at all true, but another thing you've got to understand about America is that we see only two sides to everything, pick a side, and defend it with the best mental battlements we can build with our head buried firmly in the ground, but I digress: lets say we've got two kinds of people.
There's the progressives who see the difficulty that America faces now and want move forward into the 21st century on the back of new ideas, and then there's the conservatives who see the difficulty America faces now and think the solution can be found in the 1950s... probably because they were alive during the 1950s, when we had a fairly awesome post-WW II economic boom [http://economics.about.com/od/useconomichistory/a/post_war.htm].
We flip-flop between these two ideologies every 4 to 8 years depending on who's been voted into power.
When the conservatives are in charge, they throw us into wars to try to recreate the WW-II boom (which has failed during each and every attempt but made their buddies in the arms and oil industry rich) and fearmonger a war on anarchists/communists [http://en.wikipedia.org/wiki/Red_scare]/drugs [http://en.wikipedia.org/wiki/War_on_drugs]/terrorists [http://en.wikipedia.org/wiki/War_on_terror] or whatever else they think will terrify the voter because a scared voter is a conservative voter. Eventually people get apathetic towards this approach, begin to question why it is that legislation that seems to be favoring the rich doesn't do what everybody said it would do [http://en.wikipedia.org/wiki/Trickle-down_economics] and start to vote progressive.
When the progressives are in charge, all of a sudden we're faced with the fundamental problem that change is hard. It's unexplored territory, after all, and getting it right the first time is not always feasible. People get discouraged and start pining for the good ol' days, or scared that the people in the oval office are incompetent. On the other hand, if a candidate happens to be really good at instilling the right kind of change, it seems tragedy [http://en.wikipedia.org/wiki/JFK_assassination] or disgrace [http://en.wikipedia.org/wiki/Bill_Clinton#Sexual_misconduct_claims] befalls them, which is either a sign of incredible dirty dealing or God's will depending on who you ask. Either way, the ball is back in the conservatives' court now, and the cycle continues.
This, of course, is a gross over-generalization. However, as far as that goes, it's not an unusual pattern you'll manifest in any democratic country: rich conservative elite versus the liberal middle (and increasingly becoming) lower class, the former having reason to keep things as they are and the later having reasons to want to see things change. Considering how badly they're outnumbered, it's mostly a game of the former seeing how many of the later they can delude so they can hold on to their bloated pocketbooks. You also can't really use words like "Republican" or "Democrat" to describe them because they'll tend to switch depending on which sheep's clothing they find to be more attractive.
I guess we should feel fortunate things haven't devolved into (another) civil war. If I were in charge, I'd probably kill the whole system and convert us to a ruthless dictatorship until the masses remember why a democracy is a supposed to be a good thing again. Maybe set a "you must be this smart to vote" restriction, but then that really wouldn't go over well because everybody wants their voice heard even if they know they're dumb as bricks.