Transcript for Trump: 'I Can Be the Most Presidential Person Ever' Other Than Lincoln

Reporter: Mr. President, I know you're only five days in. Has it changed you? I don't wanna change too much. I've had a wonderful life and wonderful success. I want to make this a great success for the American people and for the people that put me in this position. So I don't want to change too much. I can be the most presidential person ever, other than possibly the great Abe Lincoln, all right? But I can be the most presidential person. But I may not be able to do the job nearly as well if I do that. Reporter: Your predecessor -- used to talk often about finishing the day to get to his family upstairs. The stairwell's right over here. To have dinner with them. And I know that the first lady, mean Melania, has a big job back in New York, taking care of baron. She does, yes. Reporter: Does it make it a lonely place for you, at the end of the day? No, because I end up working longer. And that's okay. I -- I mean I'm working long hours. I mean the country has a lot of problems. Reporter: He says a lot of problems, and president trump tonight on the controversial news he has made already. Reporter: Mr. President, I wanna start, we're five days in. And your campaign promises. I know today you plan on signing the order to build the wall. Correct. Reporter: Are you going to do with U.S. Funds to pay for this wall? Will American taxpayers pay for the wall? Ultimately it'll come out of what's happening with Mexico. We're gonna be starting those negotiations relatively soon. And we will be in a form reimbursed by Mexico which I will say -- Reporter: So they'll pay us back. Yeah, absolutely. 100%. Reporter: So the American taxpayer will pay for the wall at first. All it is we'll be reimbursed at a later date from whatever transaction we make from Mexico. Now I could wait a year and I could hold off the wall. But I wanna build the wall. We have to build the wall. We have to stop drugs from pouring in. We have to stop people from just pouring into our country. We have no idea where they're from. And I campaigned on the wall. And it's very important. But that wall will cost us nothing. Reporter: But you talked -- often about Mexico paying for the wall. And you, again, say they'll pay us back. Mexico's president said in recent days that Mexico absolutely will not pay, adding that, "It goes against our dignity as a country and our dignity as Mexicans." He says quiet simply they're not paying. David, he has to say that. He has to say that. But I'm just telling you there will be a payment. It will be in a form, perhaps a complicated form. And you have to understand what I'm doing is good for the united States. It's also going to be good for Mexico. Reporter: What are you gonna say to some of your supporters who might say, "Wait a minute, I thought Mexico was going to pay for this right at the start." Well, I'd say very simply that they are going to pay for it. I never said they're gonna pay from the start. I said Mexico will pay for the wall. Reporter: When does construction begin? As soon as we can. As soon as we can physically do it we're -- Reporter: Within months? I would say in months. Yeah. I would say in months. Certainly planning is starting immediately. Reporter: I wanna ask about undocumented immigrants who are here -- in this country. Right now they're protected as so-called dreamers -- the children who were brought here, as you know, by their parents. Should they be worried that they could be deported? And is there anything you can say to assure them right now that they'll be allowed to stay? They shouldn't be very worried. They are here illegally. They shouldn't be very worried. I do have a big heart. We're going to take care of everybody. We're going to have a very strong border. We're gonna have a very solid border. Where you have great people that are here that have done a good job they should be far less worried. We'll be coming out with policy on that over the next three to four weeks. Reporter: So Mr. President, will they be allowed to stay? I'm gonna tell you over the next four weeks. Reporter: I wanna ask you about something you said this week right here about the white house. You brought in congressional leaders to the white house. You spoke at length about the presidential election with them, telling them that you lost the popular vote because of millions of illegal votes. 3 million to 5 million illegal votes. That would be the biggest electoral fraud in American history. Where is the evidence of that? So let me tell you first of all, it was so misrepresented. That was supposed to be a confidential meeting. And you weren't supposed to go out and talk to the press as soon as you -- but the Democrats -- viewed it not as a confidential meeting. Reporter: But you have tweeted -- about the millions -- Sure. And I do -- and I'm very -- I mean it. But just so you -- it was supposed to be a confidential meeting. They turned it into not a con -- number two -- the conversation lasted for about a minute. They made it -- somebody said it was, like, 25% of the -- it wasn't. It was hardly even discussed. I said it. And I said it strongly because what's going on with voter fraud is horrible. That's number one. Number two, I would've won the popular vote if I was campaigning for the popular vote. I would've gone to California where I didn't go at all. I would've gone to New York where I didn't campaign at all. I would've gone to a couple of places that I didn't go to. And I would've won that much easier than winning the electoral college. But as you know the electoral college is all that matters. It doesn't make any difference. With that being said, if you looked at voter registration, you look at the dead people that are registered to vote who vote, you look at people that are registered in two states, you look at all of these different things that are happening with registration. You take a look at those registration for -- you're gonna find, and we're going to do an investigation on it -- Reporter: But three to five million illegal voters? Well, we're gonna find out. But it could very well be that much. You have people that are registered who are dead, who are illegals, who are in two states. You have people registered in two states. They're registered in a New York and a New Jersey. They vote twice. There are millions of votes, in my opinion. Now -- Reporter: But again -- I'm gonna -- investigation. David, David. Reporter: So you're not -- I want it to be legitimate. Of course. But when you are saying in your opinion, millions of votes, that's fundamental to our democracy, a fair and free election. Sure. Reporter: You say you're gonna launch an investigation. Sure, done. Reporter: What you have presented so far has been debunked. It's been called-- No it hasn't. Reporter: -- False. Take a look at the peer reports. Reporter: I called the author of the peer report last night. And he told me that they found no evidence of voter -- -- fraud. Why did he write the report? Reporter: He said no evidence of voter fraud. Excuse me, then why did he write the report? Somebody -- pew report. Then he's -- he's groveling again. You know, I always talk about the reporters that grovel when they want to write something that you want to hear, but not necessarily millions of people want to hear, or have to hear. Reporter: So you've launched an investigation? We're gonna launch an investigation to find out. And then the next time -- and -- and I willay this, of those votes cast, none of 'em come to me. None of 'em come to me. They would all be for the other side. None of 'em come to me. But when you look at the people that are reg sistered. Dead, illegal, and two states. In some cases, maybe three states. We have a lot to look into. Reporter: House speaker Paul Ryan has said, "I have seen no evidence. I have made this very, very clear." Senator Lindsey graham saying, "It's the most inappropriate for a president to say without proof. He seems obsessed with the idea that he could not have possibly lost the popular vote without cheating and fraud." I wanna ask you about something bigger here. Does it matter more now -- There's nothing bigger. There's nothing bigger. Reporter: It is important because -- Let me just tell you, you know what's important, millions of people agree with me when I say that if you were to looked on one of the other networks and all of the people that were calling in they're saying, "We agree with Mr. Trump. We agree." They're very smart people. Reporter: Let me just ask you, you did win. You're the president. You're sitting -- That's true. Reporter: -- Across from me right now. That's true. Reporter: Do you think that your words matter more now? Yes very much. Reporter: Do you think that that talking about millions of illegal votes is dangerous to this country -- No not at all. Reporter: -- Without presenting the evidence? Not at all because many people feel the same way that I do. And -- Reporter: You don't think it undermines your credibility and-- No I do not because they would -- they didn't come to me. Believe me. Those were Hillary votes. Reporter: Mr. President, I just have one more question on this. And it's -- it's -- it's bigger picture. You -- you took some heat -- after your visit to the CIA in front of that hallowed wall, 117 stars -- of those lost at the CIA you talked about other things. But you also talked about crowd size at the inauguration, about the size of your rallies, about covers on "Time" magazine. And I just wanna ask you when does all of that matter just a little less? When do you let it roll off your back now that you're the president? Ok, so I'm glad you asked. So I went to the CIA, my first step. I have great respect for the people in intelligence and CIA. I'm -- I don't have a lot of respect in particular one of the leaders. But that's okay. But I have a Lotta respect for the people in CIA. That speech was a home run. That speech, if you look at fox, okay. I'll mention you -- we see what fox said. They said it was one of the great speeches. They showed the people applauding and screaming and -- and they're all CIA. There was -- somebody was asking Sean -- "Well, were they trump people that were put --" we don't have trump people. They were CIA people. That location was given to me. Mike pence went up before me, paid great homage to the wall. I then went up, paid great homage to the wall. I then spoke to the crowd. I got a standing ovation, in fact. -- Gotten -- Reporter: You would do the same speech if you went back -- Absolutely. Reporter: -- In front of that wall? People loved it. They loved it. They gave me a standing ovation for a long period of time. They never even stay down, most of them, during the speech. There was love in the room. You and other networks covered it very inaccurately. I hate to say this to you and you probably won't put it on but turn on fox and see how it was covered. And see how people respond to that speech. That speech was a good speech. And you and a couple of other networks tried to downplay that speech. And it was very, very unfortunate that you did. Reporter: I am curious about the first full day here at the white house, choosing to send the press secretary out into the briefing room, summoning reporters to talk about the inaugural crowd size. Does that send a message to the American people that that's -- that's more important than some of the very pressing issues? Part of my whole victory was that the men and women of this country who have been forgotten will never be forgotten again. Part of that is when they try and demean me unfairly, because we had a massive crowd of people. We had a crowd -- I looked over that sea of people and I said to myself, "Wow." And I've seen crowds before. Big, big crowds. That was some crowd. When I looked at the numbers that happened to come in from all of the various sources, we had the biggest audience from history of inaugural speeches. I said the men and women that I was talking to who came out and voted will never be forgotten again. Therefore, I want to allow you or other people like you to demean that crowd and to demean the people that came to Washington, D.C. From faraway places because they like me. But more importantly they like what I'm saying.

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