Wrestling with pigs
If you can stand it, I'd recommend reading this post over on Free Republic. It is from a freeper who infiltrated a Clark meetup on Monday and did the best he could to disrupt the meeting.
I run one of the local Dean meetups and have done so for about eight months now. I can't say that we have never been infiltrated in a similar manner, but we've never had to deal with the kind of things this guy did. I've thought about how I would deal with such a situation if it ever came up and decided that I would try to step into the conversation and say that getting into long and involved discussions about whether Bush should or should not be President was NOT the point of the meeting. If people wanted to talk about it further they could continue after the meeting. In the meantime, we need to get back to what we are really here to discuss.
The mistake the Clarkies made was in getting to involved in trying to convert the unconvertible and not spending enough time talking about their candidate and what they can do to get him elected. This is good advice for dealing with anyone who hasn't been persuaded over to your guy (whoever he may be). Hold a friendly discussion, but don't let yourself get side-tracked into a meandering debate.
The old aphorism about wrestling with pigs still applies: you just get dirty and it annoys the pig so why bother?