because in the book and in your interview, bolton claims he heard first-hand from the president that security aid to ukraine was directly linked to requests to investigate joe biden and others. so, why now? instead of when congress and many americans wanted to know the answer to this. >> reporter: well, david, he says he did not like the way the democrats were running the hearings and didn't think his testimony would make a difference. that is something i press him on repeatedly in our interview and, by the way, david, bolton is not at all surprised that the president is trying to stop the release of the book. david? >> martha, thank you. and of course, that takes us straight to the white house tonight and their effort to halt the release of this book. let's get right to our chief white house correspondent jonathan karl, who has been reporting on this. and jon, what are your sources telling you now? how concerned is the white house about bolton's book? mi a long time, d eyavid, of are waging an all-t counterattack, accusing bolton of cashing in and saying he is simultaneously making things up and revealing classified