The tempo of a townhall-style debate can be hard to control, because you never know what will be on the voters’ minds. McCain usually does well in this format, but occasionally has off days and doesn’t do well with the economic subject matter that is likely to dominate.

All Obama has to do is be likable, competent, and non-condescending. McCain has the tougher challenge because he’s behind. If he wants to do well, he could do worse than listening to Bill McGurn: hammer away at tax increases, run against the unpopular Democratic Congress, and remind voters what happened the last time a Democratic presidential candidate promised a middle-class tax cut. But he’ll have to be careful: a lot of those voters wouldn’t mind having the 1990s economy, which is Obama’s obvious retort.