Both the Obama campaign and the McCain campaign are by now pretty certain their nominee will be their party's candidate.
The next round - bipartisan mudslinging rather than intramural backstabbing - is already beginning to take shape. Obama is to be painted as a surrendercrat who will make Americans less secure but and McCain will be portrayed as Bush on crack - advocating war forever and thus making America less safe by creating endless enemies while making no real changes to Bush's other main policies.
It strikes me that the same things would be said no matter who was the frontrunner for each party at this stage and we're going to have a reprise of this long-running debate between left and right as the main feature of the presidential campaigns no matter what. The trade off is between a security clampdown born out of fear and freedom born out of the courage to be less secure thereby. It's a debate not just about what Americans do, but who they are.