The New York Times' Katherine Seelye has a solid preview of tonight's second debate between Barack Obama and John McCain. Her discussion of what is at stake for each candidate seems basically right:

Mr. McCain needs to add something to his formula if he is going to change the dynamics of the race. So watch for him to try to steer the conversation toward the doubts that he and Ms. Palin have been raising on the campaign trail about Mr. Obama's character and judgment.

Mr. McCain said of Mr. Obama on Monday: “My opponent's touchiness every time he is questioned about his record should make us only more concerned.” Expect him to follow that line of attack tonight.

As for Mr. Obama, watch for him to continue to try to link Mr. McCain with President Bush as he makes the point that most voters think the country is headed in the wrong direction.

He may also repeat his words from the first debate, when he called the financial mess "a final verdict on eight years of failed economic policies promoted by George Bush, supported by Senator McCain."

Mr. Obama also won points in that first debate, according to opinion surveys, for not shooting back when Mr. McCain fired at him. While pundits thought he had missed some opportunities, many voters thought he appeared above the fray.

Look for him to try to hold that ground tonight -- unless Mr. McCain comes on too strong.

A few of my own observations:

• Because Obama is clearly leading this race, nationally and in the swing states, he need not win any of the two remaining debates because ties go to the (front)runner.
• I wish I knew for sure whether the non-verbal aspects of a town hall format favored one candidate or the other. But I just don't have a solid hunch about this. On one hand you have Obama's physical charisma -- he is tall and sinewy, and carries himself with physical confidence. But I am never quite sure to what degree McCain's POW injuries compensate by creating an empathy toward him. I'd be curious what Salon readers think about how the debate will play out visually.
• Tom Brokaw, who emerging as the left's Gwen Ifill, could be a real wild card. (Though with far less complaining from liberals than we saw from conservatives about Ifill.) Brokaw has acted erratically in some of his television appearances recently, interjecting without prompting or cause some weird clarifications, like this one a few days ago. Some are starting to wonder aloud if Brokaw, especially following his attempts to bottle up Keith Olbermann and Chris Matthews, is revealing a not-so-subtle bias toward McCain and the Republicans.