Well, the thing I am struck by is that the republicans are such fearmongers. And it is so obvious that they are doing this because they don't want to have to discuss the issues. It's easier for them if they get the public off the issues and distracted. (the was what the Palin announcement did, that was what McCain's crisis suspension and attempt to call of the debate).
So, I've found it incredibly effective to tell them not to be so fearful and hateful and then I bring the discussion onto an issue. Like, for example, the financial/economic national international mess we are in and how on earth they think McCain's plans, which are Bush's plans to the letter. And then it's relevant as heck to bring up Keating!
Irritates them endlessly not to be able to get us off the issues!
Whenever possible, be kind. It's always possible.