John McCain went into last night's debate as the Republican front-runner against Mitt Romney, with Mike Huckabee and Ron Paul standing by. Before tonight's Democratic debate, Hillary Clinton's lead over Barack Obama appears to be slipping. McCain and Romney are competing to lead a party now sharply divided between moderates and conservatives. Are Obama and Clinton different enough to expose gulfs between Democrats? Will this week's debates make a difference? What's at stake next week when Super Tuesday creates the equivalent of national campaigns for both parties?