Finished reading Daniel Kahneman's Thinking, Fast and Slow recently. Also, there was discussion on blogs I follow about whether Gingrich was using "dog-whistle" language in calling Obama a "food stamp president".
Kahneman's fast thinking is his System 1, which occurs unconsciously as we assess our environment on a second to second basis. It is very capable, but sometimes faulty. System 2 is essentially rational, conscious thought, which we hate to do and takes will power and energy.
An example is the famous optical illusions where two straight lines of equal length are displayed simultaneously, but one looks like this >----< and the other like this <----> . When they're one above the other, the second looks shorter than the first. That's the assessment of System 1. Anyone who has encountered the illusion is capable of pulling from memory the fact that it is an illusion, and the lines are of equal length--that's System 2.
I'm thinking similar effects operate with political language. Some language creates knee jerk reactions with the partisans, it's been devalued. Things like "welfare queens", "socialist", "redneck", "Bible-thumper" all work that way.