Diuretic,
Here's what I think has happened. At some point the conservative elite decided to go all out against the left. It probably started back during the red scare, but I haven't been following that long. They developed a strategy of demonizing rather than disagreeing with opponents. It's a lot easier to paint someone in a bad light than to rationally defend one's views in reasonable discussion. Why argue reasonably when you can just call each other names?
In the short run, it seemed to work. Once the echo chamber was going full swing, the strategy immediately began paying dividends. A less informed American public began to soak up this endless stream of fear-mongering, hate, and spite directed at their opponents. But we don't require an IQ test for public office in the U.S. And suddenly, in an environment where you have your conservative "stars" publishing best-selling books with titles like "Treason: Liberal Treachery from the Cold War to the War on Terrorism", "Deliver Us from Evil: Defeating Terrorism, Despotism, and Liberalism", and "The Enemy Within: Saving America from the Liberal Assault on Our Churches, Schools, and Military" you have a great many conservatives, including those who may be in office, buying their own propoganda. Then there is no reasonable discourse, but instead have created a conservative ideology with fanatics as loyal and unreasonable as any religious fundamentalist (especially when it is intertwined with pre-established religious ideology- but that's another post). Now, we are seeing some of the elite conservative intellectuals who I don't believe were fully aware of the monster they were creating, starting to try to turn down the intensity. But what they fail to realize is that when you feed propoganda to the masses in a democracy, those that buy it are going to elect and support others who buy it and the moderates who initially benefited from this approach find that their power is slipping away and there is nothing they can do to control it.