I think things will get quite out of hand, because, as conservative in nyc said, "These people have been itching for a repeat of Chicago 1968." Bush can put Kerry on a really hard spot by insisting that Kerry condemn these extremists. That will give Kerry the choice between alienating his leftist base OR alienating middle America. It's a lose-lose situation for Kerry.
That is why I am hoping that the protests go over the top. If they do, put some serious money on a Bush landslide (if you are into strategic betting)!