He's pretty much done.
I guess ...
A comeback would be a surprise. The Hillary team has successfully sent Trump into the Khan trap and managed not only deflect her Iraq War vote and turn it against him, but also managed to deflect her email problems and turned it against him ("Russia, plz spy on us and hack us !").
There was one poll that just came out that showed him ahead in a state that he absolutely needs to win the presidency (North Carolina). I mean, other polling data shows him behind, but this single state poll could be a turning point for him!