“Which is late summer, when many a campaign has fallen behind by being defined by the opposition.”
You are trying to be just a bit too analytical. The opposition can’t define Trump because he has a four year record now. And, the opposition has already spent four years and countless money (most in free MSM contributions and efforts) trying to define Trump without much success.
We aren’t also defining the opposition, however. The media is. It’s a two edged sword. Ads running nationally claiming Trump is going to eliminate Medicare and Social Security running unanswered is not a good thing. A significant number of people will in fact be influenced by them.