professor halderman: not just me.ast 15 years there have been computer science studies looking into the security of voting machine, and the overwhelming conclusion is that american voting machines just are not built in a way that is secure enough to keep out the bad guys. emily: now, is there real worry in hacking the actual machine and changing the vote count, or hacking voter registration and just making it harder for people to vote? professor halderman: those are both problematic areas. you could hack voter registration systems, so people show up on election day and find they are not on the rolls, but i think it would be even more devastating if someone could get into the voting machines themselves and even change who won. that's what keeps me up at night. emily: do you believe that has happened? so far we have seen evidence of robust meddling, as dan coats said earlier, but no concrete evidence the vote count was actually changed? professor halderman: there is no evidence the 2016 vote count or any previous americ

halderman, the chief of staff, i told them what i was going to do after i fail ed to convince the president to stop the cover-up, and i said that somebody has to go to talk to the lawyers about this, and the prosecutors, and this thing has to end. i tried to convince my colleagues that we should all go to the grand jury. i could not sell it. >> we are looking at live pictures of the president as he is returning home from his weekend in new jersey. this is at joint base andrew, and we can see the first lady and barrett coming down the starts. and so, john dean, when the president calls you a rat in capital letters as you point out, is there any kind of strategy in him going after you and trying to villainize you? >> it could be, because he might be trying to give a warning to others on his staff. don't go in and tell the truth, or i will tarnish you and attack you. he likes to use pejoratives and name calling, and it is his sort of standard operating procedure, and i am frankly delight ed to e on his enemy's list if i have made it that far. >> i am curious also to get your take on this argum

and after he's been reelected, before that i had one meeting with halderman on this subject with the president in september. but then he starts calling on me in late february of '73 and we have a number of meetings. and when i think i have his confidence i try to convince him that we've got to end the cover-up. that's the day i really met richard nixon. he didn't want the cover-up to end because he knew it implicated not only his top aides but implicated him as well. >> lanny davis, attorney for long time trump attorney cohen, he's been reaching out to you regularly. can you tell us anything about those conversations? >> yes, i can. i met lanny during the clinton-lieu wclinton, lieu w ruwinsky proceedings. when he took on as a client michael cohen he had a number of question to refresh his recollection he wanted to ask me about. and i was willing to share that with him. he didn't indicate to me any of the testimony of his client or where he was going or what his plans were, but i was more than willing to share that history. i'm hopeful someone like michael cohen can do what i did and

what i found in the library were notes from bob halderman, nixon specifics him to keep anna chinault working on the vietnamese. for a biographer, believe it or not, that was pretty much as much as i kneaded to know. that was a glimpse into nixon's character. how far was he willing to go? the historian has to answer a question which is still unanswered, and if there are young historians in the audience want to write a great book there's still a lot of things we don't know about that story. the most important is we don't know what the effect was on president tu's government. in saigon there were all sorts of conflicting domestic opinions about whether they should join these talks. was the nixon message a tipping point? was it totally irrelevant to domestic political concerns? we don't know that, and maybe in the next 20 or 30 years we'll start getting the cables and more declassified information from the national security council, and we can make that judgment. we don't know anything about nixon's appeal to the taiwanese to open up a second front of reaching out to president tu, which