all you gotta do, is say that Biden is a fool, and say you won't dignify it with a remark, and then pivot to blast Clinton on Obamacare premiums and emails. Then you make Biden the schmuck and stay on the message you need to send.
Instead, you (again) get manipulated off message.
This is exactly the reason you can't be president, you are too easily manipulated to do things which aren't what you should be doing.
http://www.cnn.com/2016/10/25/politics/donald-trump-joe-biden-fight/index.html