Transcript for Comey says his assumption Clinton would win was 'a factor' in email investigation

Hillary Clinton's convinced that that letter defeated her. But he's there. I hope not I I don't know I honestly don't know I sure hope not but the honest answer is he wouldn't change the way I think about it. In my hope I didn't write the book for this reason but talking about leadership it was important to tell you know story because it's me trying to figure out how to lead well. The people will read that story. And try to put themselves in my issues try to realize that I'm not trying to help a candidate or hurt a candidate I'm trying to do the right thing. And you can come up with different conclusions reasonable people would have chosen a different door for reasonable reasons. But it's just not fair to say we re doing it for some legitimate reason. But it but it's some level wasn't the decision to reveal. Influenced by your assumption. That Hillary Clinton was going to win and you're concerned that she wins this comes out several weeks later and then that's taken by her opponents to sign that she's an illegitimate. President. It must have been I don't remember consciously thinking about that but it must've been because I was operating a world where Hillary Clinton was going to be Donald Trump. And so I'm sure that it that it was a factor I guess I don't remember spelling it out but it had and that. That she's going to be elected president in a fight hide this from the American people. She'll be illegitimate the moment she's elected the moment this comes out if you knew that letter would like talent from its Tilson. I would I would think that was a question asked by one of my best people. Deputy General Counsel of the FBI who was a very thoughtful quiet person didn't speak clocked. And that that morning we are making that decision she asked should you consider that what you're about to do me hopefully Donald Trump president. And I paused and I said. Thank you for asking a question it's a great question. That the answer is not from moment. Because down that path lies the death of the FBI as an independent force and American life. If I ever start considering whose political fortunes of the affected by decision we're done. We're no longer that group in America that is a part. From the partisans and that can be trusted we just another player in that in the tribal bow there's a there's no precedent from. Putting that information like this at the end of the campaign I've never heard of before right I. As I say in the book right. I think I did it the way that it should have been done I'm not certain of that other people might have had a different view I pray to god no future FBI director ever asked to find out.

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