To what extent is the tone of political discourse affected by economic conditions?

Yesterday I said I wouldn't get into it again here, but obviously I lack self-restraint. I am speaking specifically about the U.S. but feel free bring in other countries if you wish.

Fairly often you hear the complaint that the level of intolerance in political discourse is growing steadily in the U.S. -- that people now find it far more difficult to simply disagree with those who hold different opinions, and are far more likely to demonize them as "evil" and irredeemable. The first question, I guess, is whether this is really true? If so, is it part of a more or less linear progression, or is it a swinging pendulum?

And, finally, to what extent is this "intolerance" a result of, say, issues of social psychology (post-9/11 trauma, discomfort with the war in Iraq and relations with Iran, a general uneasiness about the economy and energy prices) -- in other words, if the economy picked up, there was some kind of (miraculous) graceful exit from Iraq, etc. would we be nicer to each other? The alternative answer - and probably easy one - is that if we see intolerance, it's because it is somehow inherent in the political philosophies that dominate discourse (ie., neoconservative/fundamentalist).