I study political advertising, and I think I can shed a small amount of light on the GOP advertising approach. From the outside, it looks like rapid-fire distraction and smoke-screen. But having studied some of the effects and the symbolism in these ads, I think I can offer something valuable here. Three things are going on, inoculation, disaffection, and distraction.
Regarding inoculation, the McCain people have had to re-code the meaning of Palin. Lakoff would argue that it is important for the GOP to frame her in way that is favorable to GOP prospects. The problem is, she's been lying. The bigger problem for the GOP is that the media began to make a theme of this in coverage. The latest GOP spot, the "Desperate" spot, is an effort to contextualize claims of lying in a narrative that has Obama and Co. attacking in various ways. So, they are struggling to keep the maverickiness despite the lying, giving it a positive meaning - something like, "Strong woman overcomes black man's lies."
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Regarding disaffection, the problem McCain, and Republicans generally, have is that they are out-numbered. This is particularly pronounced this year, so they can either throw in the towel, get Democrats to vote for a Republican, or find a way to anger voters so that they don't want to vote at all. Effects research shows that negative advertising has a number of influences, but one is to disappoint voters. The effect of disappointed voters is that they become less likely to come out to vote. I firmly believe that the rapid-fire negative spots by McCain have less to do with reinforcing a theme - because they don't - and more to do with causing voters to think this is a negative and nasty campaign. Centrists in this election who don't vote are better than those that do. It helps level things out some for McCain, and may also help in statewide elections.
Finally, and this is related to disaffecting voters, it is to McCain's advantage to distract voters from Obama's themes. If they can get Obama to respond in kind, they can reinforce the impression of a negative campaign AND knock Obama off message. So, they keep heaping crap at Obama with the hope that he won't keep weaving into his reply, "That's not change," "Or that's no different than the last eight years." Obama has been handling this with aplomb.
There are calls for Obama to be more aggressive. But, if framed properly, McCain's campaign can be framed as self-destructing as a result of these spots and the Palin choice (another attempt at distraction). Obama has remained on message, and is starting to influence media coverage of McCain as a desperate liar.
Don't get angry at Obama for not wallowing in McCain's mud. Sure, he could strike back hard if he wanted to, but I think he has been. This is a message that has been test marketed for 19 months now. It resonates, and it will resonate with enough people to tip this thing. I'm comfortable now in my belief in that.