The first debate between John McCain and Barack Obama is scheduled for Friday night, but its unclear whether it will happen because McCain wants to delay it while Congress deals with the financial crisis. Whenever it happens, there are plenty of clues about what to expect from the candidates — based on their performances during primary season.

Each camp has studied all of the previous debates closely, and each will try to exploit the other's weaknesses. McCain will try to get Obama to seem aloof or too intellectual. Obama will try to push McCain to be overly aggressive and to seem uncontrolled.

The topic for Friday's debate in Oxford, Miss., is foreign policy, an area where their views differ markedly — most notably on Iraq.

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