Trump and Clinton are both very fortunate in that they're both running against the only opposition candidate they have a chance of beating. It's very sad that the absolute worst candidate from each party won the nominations.
Ultimately I expect the debates will lose it for Trump. Mudslinging, playground fighting and insults might work in an internal party primary where you're preaching to the converted, but that tactic won't work on the national stage when you're vying for independents. Having said that, Clinton needs the Sanders supporters and she's doing a bang up job of alienating them at the moment.