Second, McCain has set a high bar for himself that he probably cannot possibly meet. When the country sees that McCain was all talk, it will hurt McCain even more than if he hadn't made any predictions about the outcome of the debate at all. Moreover, McCain's prediction will increase the audience for a series of debates that have coincided with plummeting polling numbers for John McCain.
And tonight's debate format doesn't favor McCain, who has been unable to look Obama in the eye in past debates. The Washington Post points out that, "Unlike the two previous presidential debates, tonight's encounter will feature the two candidates seated at a table with the moderator." McCain is far more likely to get rattled and lose his cool, or seem angry and petulant, in this format than is Obama.
Third, McCain's bluster shows that he is desperate and that his supporters are egging him on to do something about the desperate state of his campaign. His promise to whip Obama is effectively a concession that he has failed to do so in past debates, and in the campaign in general.
If John McCain were smart, he'd have encouraged viewers not to watch the debates at all, since there's no evidence that the debates have done him any good. But, he might be of the opinion that the campaign is already effectively lost, based upon recent polling, so he has nothing to lose by promising that something will happen in tonight's debate that McCain has failed to accomplish in all the debates that preceded it.
I've found all of these debates to be ultimately pretty boring. Barack Obama has shown himself to be strong and steady, not surprising and making very little news through these debates. Meanwhile, McCain has meandered through his answers, calling the audience "my friends" in a way that is really annoying to those of us who don't consider him to be a friend of ours, including many Republican, Independent and undecided voters.
I'll watch tonight's debate but, with Obama in the lead and quietly trying to convince undecideds while running out the clock, it's hard to see how anything that happens there can be more monumental than the melt-down in the US and world economy that has dominated the news for the last few weeks.
Obama will keep doing what he has been doing in the last debates (making little news but seeking to reassure voters), while McCain may make a desperate move that will turn voters off even more than they already are - to him, to George W. Bush, and to their deregulated anything-goes banking, mortgage and health care systems.
The real news for the weeks leading into the General Election will be whether the candidates can get their voters to the polls and the Election Day chaos and spurious legal challenges to the final results that Republicans are preparing to submit to courts packed with Bush appointees.