(Disclaimer: I can't stand either candidate; I'm somewhat reluctantly #TeamGaryJohnson as of right now.)
No. People have been underestimating Trump every step of the way. He's absolutely a jackass, and he is going to continue saying stupid shit. But his main focus is going to be attacking Hillary. She hasn't been attacked yet. Sanders (probably to his detriment) kept his distance for the most part.
I know HIlldawg-gaf (and most of the mainstream media) have already decided none of Clintons vulnerabilities (Benghazi, Clinton Foundation, emails, Slick Willie's escapades, among others) matter. But sitting in an echo chamber repeating that none of it matters doesn't mean much outside the echo chamber on the debate stage.
Trump has a lot of ammunition, and for as bad as his negatives are right now, Hillary's aren't much better. And her supporters strutting around claiming "anyone who supports Trump is automatically a bigot" (I see a lot of that on this site) aren't exactly going to win anyone over that way.
As of now I'd guess Trump will probably come up short. For as awful a candidate Hillary is, Trump is, well, Trump. But I see little/no chance of a landslide. I think we'll see a map pretty similar to 2012, but Trump has a shot at doing well in the rust belt and potentially stealing Ohio and/or Pennsylvania (though he could lose a couple states Romney won).
The debates will be interesting.