GOP presidential front-runner Donald Trump is making a last-minute push to try to triumph in the key early-caucus state of Iowa, a race which his rival Ted Cruz has long been favored to win.

The real-estate tycoon, on Jan. 24, urged his backers to turn out to vote in the Feb. 1 caucuses, though, true to his style, he was already predicting victory, CNN reported. And one by one, he ripped his Republican competitors in a Muscatine, Iowa, campaign rally, the news channel noted.

Addressing ethanol production, a critical issue for Iowa's agricultural community, Trump alleged that the Texas senator was more interested in backing one of his home state's key industries.

Trump: 'Forget' Cruz support for ethanol

"Cruz is getting oil money," Trump said. "He is so against ethanol, you can forget it," noting Cruz's position in favor of phasing out the mandated ethanol fuel levels in gasoline, which have long served as a boon to Iowa's economy.

And referencing the poor poll numbers of Jeb Bush, often seen as the GOP's main "establishment" candidate, Trump proceeded to offer some advice to the former Florida governor.

"It's time to give up, Jeb. It's time to give up," he said. "In life, sometimes you have to admit it when you don't have it."

Key newspaper endorses Rubio

Iowa's largest and most influential newspaper, the Des Moines Register, meanwhile, is urging GOP voters to back Florida Sen. Marco Rubio -- and not Trump -- in the Feb. 1 caucuses.

As it endorsed the Cuban-born senator, the paper's editorial board urged Republicans not to back the "anger, pessimism and fear" it says Trump has peddled during his campaign.

Nevertheless, a Jan. 21 survey conducted by CNN and the Opinion Research Corporation (ORC) suggested that Rubio is currently only backed by 14 percent of likely caucus-goers, while Trump is supported by 37 percent and Cruz by 26 percent.

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