Transcript for Donald Trump on 'This Week'
every august, the iowa state fear features pork tenderloins, deep-fried twinkies, a whole bunch of ambitious politician with the white house in their sights. It's three years away, but it's never too early. Presidential hopefuls are out in force across the hawkeye state this morning. Jonathan karl is there. Reporter: Good morning. Donald trump was here, he gave a speech saying that passing immigration would be a death wish for the republican party. He may run, but that has some people raising their eyebrows and some rolling their eyes. Could you be taken seriously? I have built a great company with a tremendous net worth. And beaten a lot of people that are very smart. And that's what the country needs. Reporter: What do you say that a possible trump candidacy is a joke? It's a publicity stunt, to get more attention for yourself? Interestingly, I filed applications last time, and i filed my net worth. I'm a private person, nobody knows. People were shocked at the number. Now it's bigger than it was. How strong the company is, how much cash. It's a beautiful company. It's a company like this country should look. Reporter: What's the number, what are you worth now? Probably over $10 billion. Reporter: If you were to run for president, how much would you be willing to spend? spend a lot. Reporter: A modern presidential campaign would be half a billionrs. It could. Or more. Reporter: That much? If I did it, I would spend what it took. Reporter: Your assessment on the field. Give me the first word that pops to mind. Marco rubio. Immigration. Reporter: Rand paul. Interesting. Reporter: Paul ryan. Well, you know, I really like him a lot. But you have to look at what he says about the social security and medicare and medicaid. It's a tough road. But I do like. Let's say medicare. Reporter: Chris christie. Wonderful person. He's a wonderful guy. Reporter: Ted cruz. Obamacare. He really is fighting on trying stop this absolute disaster for the united states called obamacare. Reporter: Donald trump. Smart. Reporter: You said a lot of things over the years that people say make you not serious. One of the big things is on the birth certificates. Why does that make me not ses? I think that resonated with a lot of people. Reporter: But you don't question he was born in the united states, do you? I have no idea. Reporter: Even at this point? Was there a birth certificate? You tell me. You know some people say that was not his birth certificate. Nobody knows. You don't know either. You're a smart guy. Reporter: I'm pretty convinced. You said pretty. Reporter: Totally convinced. You said you're pretty convinced. Let's see what happens over time, but it's not my issue, jonathan. My issue right now is much different. Wait a minute -- my issue is economic. Our country is being ripped apart by china and many other countries. That's my issue. Reporter: But on this issue -- you said you're pretty sure. You're pretty sure, that's not acceptable. You have to be 100% sure. Reporter: I'm 100% sure. I don't think you are. Reporter: Let me ask you this, ted cruise. Born in canada. If he was born in canada, is he eligible to be president of the united states? If so, he's not. Reporter: He was definitely born in canada. You'll have to ask him this. Reporter: His mother was an american citizen. That'll be ironed out. I heard somebody told me he was born in canada. That's his thing. Reporter: You played golf with john boehner the other day. I did. Reporter: The big question is will house republicans pass a funding bill for the government that includes funding for obamacare. Should they? Well, that is a good question. I do think this, the budget should be funded. But I don't think that obamacare should be funded. And the republicans are in many ways their own worst enemy. I happen to be a republican. If they get together and were unified, I think they could do damage to get rid of obamacare chas very positive thing for the country. Reporter: You know hillary clinton. I do. Reporter: How touch ever tough will she be to beat if she's the nominee? She will be tough. Reporter: What do they need to do to beat her or whatever the candidate is? They need to pick the right candidate. Mitt romney was -- in theory, everything should have been good. It didn't. Didn't resonate. Wonderful guy, didn't resonate. They have to pick the right candidate. Reporter: The iowa caucus are two and a half years away, but this place is crawling with possible presidential candidates. Just this weekend, we have seen ted cruz, of course, donald trump, rick santorum, and even claire mccaskill was out here on behalf of hillary clinton. If you're here in iowa, looks like the 2016 presidential campaign is already well underway. All right begun. Thanks very much.
This transcript has been automatically generated and may not be 100% accurate.