I listened to Don Trump (Jr.) after the debate. He's fluid, well spoken, and all I could think of was that if Don, rather than The Donald, was debating Hillary, he'd have turned her into mincemeat. But Don isn't the candidate; his Dad is. Don Trump knows how to stay on message better than his Dad. Perhaps the wrong Donald Trump is the Presidential nominee. He'd have done a better job in the General Election of getting the Trump points across of Immigration, Trade, and Foreign Policy that brought about a revolution in the GOP and still have the potential to bring about a revolution in General Election politics.
I'm pretty sure this was part of the plan from the get-go. Donald is running now to pave the way for Don, Eric, or Ivanka to take over the GOP in the ensuing decades.