Donald Trump. REUTERS/Scott Morgan Real-estate mogul Donald Trump opened up his Saturday-afternoon speech in Iowa by warning the locals there what would happen if he doesn't win their state's caucus next month.

The Republican front-runner noted that Iowa has not had a great track record of picking presidential nominees in recent history.

"You haven't been good. In fact, some people say, 'Oh, it doesn't matter if you win Iowa.' Now don't let them talk to you that way. Don't let them talk to you that way," Trump said.

He added: "You have not picked a lot of winners. And that will make me feel good only if I don't make it with Iowa."

In 2012, former Sen. Rick Santorum (R-Pennsylvania) narrowly edged out the eventual nominee, former Massachusetts Gov. Mitt Romney (R). In 2008, former Arkansas Gov. Mike Huckabee (R) won Iowa, though the eventual nomination ultimately went to Sen. John McCain (R-Arizona).

Trump has led in the vast majority of Republican-primary polls since last summer, but Sen. Ted Cruz (R-Texas) recently surged to the top in Iowa. A Fox News poll released Friday found Cruz in the No. 1 position with 27% among likely GOP caucus-goers. Trump was four points behind him. The New York Times described Cruz this week as having "plainly become the candidate to beat in the caucuses."

If Cruz wins in Iowa on February 1, Trump said that he would be highlighting the state's history of picking Republican-primary losers.

"You know that I'll be saying that big league: 'They haven't picked a winner in years!'" Trump said. "All right, but you know what, if you pick me, you're going to pick a winner. Because we're going to win. I'm telling you, we're going to win. And it's really time that that happens."

Trump also took some shots at Cruz for allegedly flip-flopping on ethanol subsidies, a popular local issue in Iowa. The Des Moines Register reported Thursday that Cruz has been dogged by questions about where he stands on the subsidy issue. Cruz, like many ideological conservatives, opposes the subsidies, but has recently started stressing that he would phase them out over several years.

"Ted isn't doing well at all in New Hampshire, but in Iowa he's doing well. And my primary opponent was totally opposed to the ethanol and the ethanol industry. Because he's with the oil industry. You know, he's from Texas. I guess it makes sense," Trump said.

"And he was getting clobbered," he recalled. "And all of a sudden he said, 'Uh, oh, I'm for ethanol.' You can't do that. You can't do that with three weeks to go. You're not allowed to do that."