Looking at it pretty simply but not, I think, incorrectly: Trump’s big problem is that too few Americans think he is qualified for the presidency, has the right temperament, etc., while Clinton’s big problem is that too few Americans think she is honest and trustworthy. She cannot do much to address her problem in a debate, and he can do a fair amount to address his. (It might help if Kellyanne Conway puts a shock collar on him.)