I think Trump is just playing the media. He is tweeting about disavowing David Duke on Friday, and on Sunday he is saying “David Duke? I don’t know him. I’m not going to disavow some group until I do some research.”
What’s the sense in disavowing anybody? You state your case and let them vote the way their thoughts direct them.
If you click through to the tweet there is a video of Trump disavowing Duke at the presser where Christie endorsed him.