Transcript for Iowa Freedom Summit Draws GOP 2016 Hopefuls
And we turn now to the race to replace president Obama. Something of a kickoff yesterday in Iowa. Packed with presidential contenders. Jon Karl was there for all the action. Reporter: And they're off. In Iowa this weekend, the unofficial start of the race for the republican presidential nomination. And it is wide open. This is the most open republican nomination since 1940. I think it will be fun. It will be interesting to watch. Reporter: Open and crowded. At least 12 speakers here at the Iowa freedom summit say they're at least thinking about running. New Jersey governor Chris Christie. You're the only person you agree with 100% of the time. Reporter: A trash-talking, sometimes moderate republican from the northeast might have a tough time in the conservative heartland. When we caught up with him exclusively, outside this secret backstage exit, he suggested Iowa could be Christie country. You feel like you can compete in Iowa? Sure. Why not? Reporter: Another blue-state governor, Scott walker, was one of the summit's biggest stars. If you're not afraid to go big and go bold, you can get results. Reporter: We met up with him moments after he got off stage. He made it clear he's getting ready to run. That sounded like a campaign speech. At least the beginning of one. We've been testing in Wisconsin. There's no doubt about that. We're looking for good leadership. We'll see what the future holds. Wow! Reporter: But judging from the reception here for Texas senator Ted Cruz -- God bless the great state of Iowa. Reporter: -- They might have found their candidate. If you say you'll stand up to the Washington establishment, the career politicians of both parties that have gotten us into this mess, show me where you have stood up and fought. Reporter: How much of a mistake would it be to nominate another establishment republican? Over and over again, when republicans have nominated candidates in the mold of Gerald Ford, bob dole, John McCain, Mitt Romney, all of whom are good, honorable, decent men, but every one of them lost. Reporter: Mitt Romney was not here. Neither some other gop stars like Jeb bush, Rand Paul, bobby jindal, and Marco Rubio. It's a good thing they missed Donald Trump's speech. You can't have bush. The last thing we need is another bush. Reporter: Yes, trump is thinking of running again. And some of the day's biggest applause lines came when he hit bush and Romney. I think Romney had his chance. He should have won. He choked. Reporter: Another target, Hillary Clinton. Like Hillary Clinton, I, too, have traveled hundreds of thousands of miles around the globe. But unlike her, I have actually accomplished something. Reporter: One of the newcomers here, Carly fiorina, former leader of Hewlett-Packard. Women are 53% of the voters. We're more than half the nation. It's important that women are in our party. Reporter: And then there's 2012 Iowa winner Rick santorum. He needs a way to separate himself among what could be the biggest Iowa field ever. How many republican candidates can you fit on a debate stage? Well, I guess that would depend on how big the stage is. Jon Karl joins us. From Iowa. Jon, a long day yesterday. I caught a lot of it on CSPAN. A lot of interesting moments. Inside the room, what was the standout? Reporter: There were a number. The biggest, Wisconsin governor Scott walker. This was his Iowa breakthrough. He became a hero four years ago by launching the occupy movement when he took on the unions. He's got a reputation for being a little dull. He's still not known well in Iowa. He was the big breakout star of this event. Okay, Jon Karl, thank you very much.
This transcript has been automatically generated and may not be 100% accurate.