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This is a RUSH transcript from "The O'Reilly Factor," September 13, 2011. This copy may not be in its final form and may be updated.

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BILL O'REILLY, HOST: In the "Factor Follow-up" segment tonight: A new poll from Rasmussen says in match-up between Mitt Romney and Barack Obama, the governor wins 43-40. But obviously many of those polled are undecided. Joining us now from Houston is Mitt Romney, fresh off the debate last night in Florida. First of all, you guys all ganged up on Rick Perry. Was that nice, Governor?

MITT ROMNEY, GOP PRESIDENTIAL CANDIDATE: You know, it's a funny thing about -- about debates. Everybody is fair game, myself included, as you noticed.

O'REILLY: So you, when you guys all ganged up on him, did you know that was going to happen? Did you know they were all going to gun for Perry last night?

ROMNEY: You know, you never know what's going to happen in those debates. You don't know what the questions are going to be. You've got an idea what the topics will be. You don't know how that's going to get developed. But I typically know that there are going to be some topics where they all come after me, and they did. And generally folks tend to focus their attention on those that are doing the best in the polls. Although polls at this stage don't tell you a lot what it's going to be like at the end. But, you know, Rick is new on the stage and gets a chance to explain his views. And if he does that well, why he'll continue to have strong support. And if he doesn't, why he'll lose it.

O'REILLY: Because he really got a beating last night from you -- all of you guys. It was interesting to watch it. Now, there are reports that there's bad blood, and I don't mean feuding or anything like that, but you know, annoyance -- that's the best word -- between you and the governor going back to the Olympics, when you were heading up the Olympics. And he wanted the Boy Scouts to be the official greeters and you said no, because they're not 18, they can't be. And you guys got into a snit. Is that report true?

ROMNEY: No, actually, because I didn't even know about that supposed disagreement...

O'REILLY: That's not true at all?

ROMNEY: ...until I…

O'REILLY: Not true.

ROMNEY: I don't think -- my memory may be a little foggy, but I don't think I ever heard from Governor Perry on this topic.

O'REILLY: OK.

ROMNEY: I heard about it once he got into the race because someone wrote about it, but I never heard from him. I do remember the controversy. Some people said, "Hey, why can't we have Boy Scouts as the volunteers at the Olympic Games?" And the answer is, "Well, Boy Scouts start at age 11, and you have to be at least 18 to be a volunteer."

O'REILLY: All right. So the media report, according to you, is bunkum. There is nothing. Then there was another report that you hired, when you were the head of the Governors Association, a consultant that was working against Perry in Texas, and he didn't like that. Any truth to that?

ROMNEY: You know, he may not have liked that. There may be a reality that there were places where we hired folks that were at cross-purpose. That probably happens in the world of politics. But, you know, we're big guys, both Rick Perry and me. We understand that now and then we'll step on each other's toes. Look at us. We're all going after one another. When this is all over, we'll all come together and support whoever the nominee is. You know, are there ever any points of friction between us? Of course. That's the nature of being in a political battle. And yet we all agree that one of us has got to replace Barack Obama and that he would be an absolute disaster to be president for another five years.

O'REILLY: Do you think -- do you think Barack Obama is the worst president in American history?

ROMNEY: I'm not enough of a historian to tell you the answer to that. I can tell you that I think he's been a very poor president. I think, actually, his failures internationally will have perhaps even longer-lasting implications for America and the world than even his failures domestically. And those, of course, stand out brilliantly. I mean, internationally, the outrage that is felt across the country for his failure is -- is well-known.

O'REILLY: But I don't understand what failure you're talking about. He got Usama bin Laden. He's dead. The drone program has downgraded Al Qaeda's ability to do anything. He has kept most of the Bush stuff in place: rendition, Guantanamo. So what disasters overseas are you referring to?

ROMNEY: Well, probably the greatest threat to the security of the world is a nuclear Iran.

O'REILLY: OK.

ROMNEY: And Iran -- and the president had an opportunity to really put pressure on Iran. In my view, he faced Russia at a time when Russia was critical to this decision. Russia had as their No. 1 foreign policy objective removing our missile defense sites from Poland. He gave them that. This president gave them their No. 1 objective.

O'REILLY: No one is going to remember that. That's small ball, but Iran is big. Iran is big.

ROMNEY: No, but my point is this. Had he gotten Russia to agree to impose tough, crippling sanctions on Iran, we could have put a lot more pressure on Iran.

O'REILLY: Well, Putin's not going to do that. Maybe you can convince Putin to do it, but Bush couldn't get anything out of Putin. None of them could.

ROMNEY: I'll tell you one thing. I would not have given them their No. 1 objective, which is removing our missile defense sites from Poland...

O'REILLY: That's fair enough.

ROMNEY: ... unless I got something like that for it.

O'REILLY: You mentioned Iran. Nobody seems to know what to do with those people over there to stop them on their nuclear quest. What would you very specifically do?

ROMNEY: Well, several years ago I spoke at the Herzliya conference in Tel Aviv and laid out seven steps. I'll try and be brief. But No. 1 was making sure that we put in place crippling sanctions.

No. 2 was communicating on the ground in Iran what the cost was to them of becoming a nuclear nation. They would be in a circle of suspects if ever a nuclear device were to be tested…

O'REILLY: They know that though.

ROMNEY: …or to be applied anywhere in the world. Number -- I'll get to the last one. No. 7 is you have to have a credible military threat. Iran is going to pursue a nuclear weapon.

O'REILLY: Like what, a blockade?

ROMNEY: You have to have credible options that Iran has to know that if they pursue nuclear folly, that there is the potential that there will be an effort on the part of the United States to remove that threat.

O'REILLY: All right. But, you know, we hear that. I heard that from Barack Obama when I interviewed him as a candidate, and still Iran continues in its quest. Finally, how are you going to...

ROMNEY: Yes, but what -- yes, but what he didn't do were any of the seven steps necessarily to actually get Iran to change its course. He did not put in place those crippling sanctions.

O'REILLY: Well certainly he hasn't gotten their attention. That's for sure.

ROMNEY: And he hasn't put together the kind of military credibility in terms of planning or communications that would suggest to them that it's anything but a hollow threat.

O'REILLY: All right. How are you going to convince conservatives, who are suspect of you -- not all of them, but some of the -- because you did the individual mandate in Massachusetts about the health care. Conservatives, that drives them nuts. They say that the government, state and federal, has no right to force anybody to buy anything. How are you going to convince those people that they should support you?

ROMNEY: Well, the government, of course, has a lot of mandates, and I know folks don't like that. But mandates kids go to school, mandates they have to have auto insurance if you have an automobile. And my conservative friends say, "Well, we don't have to have automobiles." And it's like, what state do you live in? Of course you have to have automobiles in this nation. And the plan that we put in place was one that was put together by Republicans and Democrats. It works for Massachusetts. Obamacare, however, is unconstitutional, will not work, is massively expensive. I will repeal it. By the way, I had this same position four years ago.

O'REILLY: Why is it unconstitutional? If Romneycare isn't unconstitutional, why is Obamacare unconstitutional?

ROMNEY: Because there are two different constitutions. Each state has its own constitution.

O'REILLY: OK. So the state has a right to mandate it, but the federal government doesn't?

ROMNEY: Of course. States have the right to mandate. That's why states mandate kids go to school. The federal government can't do that. States mandate you have to buy auto insurance. The federal government can't do that.

O'REILLY: All right, Governor. You're always welcome. And so is Rick Perry. We're trying to get him on the program. And we appreciate your time very much. Very interesting tonight. Thank you.

ROMNEY: Thanks, Bill. Good to be with you.

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