American politics swings back and forth, depending on current events. After 9/11, the political heartbeat was on the far right. It wasn't long after, however, that the sentiment swung back to the left, and we saw a Nancy Pelosi Congress.
After that, the Tea Party pulled the momentum back to the right in 2010, but that cycle was also more shallow and short lived. Now we're seeing a swing back to the moderate left, where America finds it's happy medium.
Republicans like to say we're a "center right" country, but I believe America finds itself most comfortable in the moderate left, and it drives them crazy.