Transcript for Dershowitz: If Trump does Mueller interview, 'he may be walking into a perjury trap'

time. Thank you. Some ass now from O legal panel.allen dersho, author of the new book, "The case against impeaching trump," and ash rangappa, former FBI special agent of New York and senior urer for global affairs and analyst at CNN. Welcome to you bot an, let mein with you. Interesting mixed message from dy Giuliani. Nothing to worry aborom Robert Mueller, yet the scorched rth against his team continues. Yeah, because thes something to worry about, obvi in the end, if the presi sits down with muellhe may be walking into a perjury trap. If he is unwilling to sit do he may be oenaed. En probably there be a year O of litigation, but in the end probably he'lle to appear in front grand jury. Great vulnerability perjra as I argue in my book, you need to commit a crime to be impeached, and if he's committed previous crimes, thereo evidence of that, that won't wo but if he commits the crime of ury, he's in Clinton land. Thatets to thequestion, Asha, the perju Trane concern. It looks like they're not go to do an inter. You heard Rudy Giuliani say that without the president testif there isobstruction case. That's not true. The ruction case does center on tresident's intent, whether he acted corruptly WHE he fired jamomey. Mur Ave a lot circumstantial evidence, the conversations between James Comey and the president, he has attemptsthe white house to approach then NSA to try stymie this investigation. He has his own worn the lestolt interview. So he does have a circumstantial se. I do thinkllts to get from his own words what the president had is mind. Do younk Mueller can write a report, make a case obstruction without interviewing president? No, I don't. Where eslly disagr is a presi -- and I argue this and I think I prove it conclusively. A president be charged obstruction of ice for merely exercising his power unr article tw he can be T way Nixon was and Clinton was -- he question is WHA going on in hinddid we haorrupt intent. You cannot question a president's motiwhhe president acts. Ifre pardons, th it. If a president fires, that's it. You can' beyond the and get into his motor into his tent. That's - president ever been -- . A pardon is a pardon. The covering of the murder M be an independent crime. Pardon cannot be tactus Reyes of a that is a constitutionally protected act. Where I disagree is that the don is an expliwer granted he constitn the firif James Comey, T firing of one of his prince officers, is an implicit power. He also has the duty to ensure that the laws be faithfully ted. So iny ways obstruction of justice is implicit in the nstitutionwell, to make suhat investions don't get thwarted forarious ends. You can't start probing the motives of presidents. All presidents have mixed motivel the time. They're political. They're idealogical.ey're patriotic. They're can I write a good book after I finish my term. When you start probing ve presidentho has acted properly under the constitution, you're really going a very, very dangerous slippery slope. Let's talk about Michael Cohen for a second. You saw Rudy Giuliani saying nothing to fear, no problem as Ng as Michael Cohen tells the truth. Do you agreeh that? Think that they have a lot toea Michael Cohen is probably the closest person in trump's inner circle and have been for many years. He was basically the fix so he's going to knoloabout what waspening not just in the campaign but in other areas such as with the stormy Daniels case, and to go back to the perjury issue, let's remember that the civil cases alsosent a problor trump. He be deposed in of those S Only if he testifies and he's not going to do that. He's not going to make the mistake hilton made. Learned that lesson. Nobody, no decwys ever going llow the president to testin a civil case. It will be resolved in another way. The problem cohes is not about the bause you can't Ute a present while he'ssiing and yon't impeach him for business dealings in the past that Cohen may know about even iere isn't im Cohen S a problem because the president were to testify, Cohen could contradict him. En you have a current perjury prosecution which is an impeace offense. That's one con. Final question though. If indeed there is S are related to the stormy Daniels case and the president is implicated in that, that was in Servi- at would the charge of getting him elected, that comes C T imacble offense. N my book I argue that th close queion whether or not you can impeach presidenr a crime that helpedet elected. Think the stormy Daniels would be a real stretch. Thaveuch. When we come back, the

This transcript has been automatically generated and may not be 100% accurate.