I've given this little thought, but what if Trump lets them know that if they want to play like that, he'll play the same way - what if he started endorsing candidates running against Republicans in contested states for Congress? I.e., "this Republican is bought and paid for by the establishment. You can see how they're attacking me - they want people in office who will do their bidding. Don't vote for this guy, he's a loser."
And then, I'd know this whole thing was orchestrated by the Democrat party - they had to have put Trump up to doing this.