-- practices appellate and constitutional law. he was under president reagan and george h. w. bush. welcome, david, great to see you. >> good to be with you. paul: let's start don mcgahn. the white house claim of a testimonial privilege. he doesn't even have to appear under the constitution because of the separation of powers. is that justified? >> it is justified, when message to chairman nadler, congressional power to obtain evidence, the context of oversight or impeachment is not unlimited. it is all because of transitional powers the case is compelling. first of all paul, we're talking about discussions between white house counsel.e there in the sweet spot, all forms of testimony and executive privilege. it is the most i can repair the other argument that's very interesting that is somewhat