There's been a lot of talk that Obama may fire off a remark early in the debate to try and get under McCain's skin. This strikes me as a potentially dangerous move for two reasons: 1) if it's not done with proper timing and tone, such a "dig" could come off badly and make Obama look arrogant and/or impetuous and 2) it opens him up to a counter punch by McCain and those can often be more effective than the initial jab.

Nevertheless, if Obama wants to say something subtle that might stick in McCain's craw and highlight the events of the last couple of days without coming off as necessarily partisan or insincere, he might try an angle like this:

"First, I'd just like to thank John for coming tonight. A few days ago he said he wasn't going to be here if there wasn't a deal done on the financial rescue plan. Even though Congress still hasn't reached an agreement I want to applaud him for changing his mind and showing up tonight so we can talk directly to the American people about the important issues facing the country."