Professor Jessica Roth told Poppy Harlow on CNN Newsroom that in terms of the President citing executive privilege, "The ship has sailed. As a legal matter, it is quite clear. He waived the privilege when he agreed to let his aides including Don McGahn sit down with the special counsel for the interviews on those subject matters."

Link to video: https://www.facebook.com/cardozolaw/videos/2569991253228302/ 

Update