McCain is tanking in the polls, so has to do the nigh-impossible in tonight's debate—get people to stop talking about the economy

In half an hour Barack Obama and John McCain meet in the second presidential debate. The pair square off in Nashville this time, in a debate moderated by veteran broadcaster Tom Brokaw.

Obama has got to be stupendously confident going into the debate. He's extended his national lead to 8 or 9 points—his best ever. He seems to have doubled his lead in Pennsylvania in just a fortnight, and has just about everything going his way in Ohio.

For a closer look at the battleground states, check out this report from George Stephanopoulos on the ABC (hopefully the link to video works). He points out that Obama has a "clear lead" in every state that John Kerry won in 2004. The Democrat is also ahead in Iowa and New Mexico. If those states all remain on track for Obama, he only needs one of the other battleground states, such as Ohio, Florida, Colorado, or Virginia to lock it up. Stephanopoulos will be somewhat cautious about predicting too much too early, but add in Obama's huge spending power and this could be a landslide unless McCain does something drastic, and soon.

The only option left seems to be to go negative, and the Obama campaign is sending out emails warning supporters they'll need to be ready to defend their guy. One email reads:

John McCain has given up talking about the issues that are central to this election -- especially the economy. Instead, he's running the most negative presidential campaign in modern history.
In the past few days, we've seen the beginning of a major offensive that McCain is about to launch, filled with distortions, personal attacks, and flat-out lies about Barack.

Tonight's town hall debate is a tough place for McCain to go on the attack though—there's no follow-up allowed from the floor or from Brokaw. But McCain has to try something to get the conversation off the economy. Check out The Fix for a run-down on what to expect.

For those of us in New Zealand, we can watch via the websites of a number of America's largest news organisations, such as the Washington Post.