If they had an actual debate, Trump would get crushed and would look like the know-nothing idiot that he is. Unfortunately, the presidential debates aren't debates at all. Remember how Sarah Palin got through her "debate" with Uncle Joe doing all canned lines? How many saw her as the winner despite being dumber than a brick wall?
The debates are a real danger to Hillary because we don't know how she would react to Trumps crazy verbal assualts on her. Of course, if they do have an actual policy debate with the moderators doing fact checking and the works, then Trump will get annihilated.
To be fair, Palin got away unscathed because Biden's handlers neutered him by forcing him to play nice to avoid looking sexist.