What makes you believe that and what would Trump have gotten out of that?
What does Trump get out of destroying the GOP (remember this guy was a rabid birther who endorsed Romney in 2012 and now you think hre really just wants to help Hilary for some reason)
If Trump hadn't done so well (which no one predicted) then what would have been the point of him running (or planting himself as it seems you're suggesting). Just to be another loser who doesn't do shit? How is that supposed to help Hilary
What makes me believe that? The fact he has systematically called all his GOP competition losers, liars, or similar to pedos would be an indication while hardly ever saying anything that strongly about Clinton.
What does he get out of destroying the GOP? His buddy Clinton in the WH.
Why plant himself? As I said, specifically to hurt the other candidates with his name calling and forcing them to commit their campaigns to specific issues and stances rather than fence-sit for more votes.
What has he gotten out of it? Who said he has to get anything out of it? What does he need? Power? Fame? Money? He already has that.
Have you ever wondered why his campaign has hurt the GOP - his own "party" - more than the opposition of the DNC?