DES MOINES, Iowa - (AP) - Unpredictable to the end, many of Iowa's GOP voters still haven't settled on a favorite candidate just hours before they cast the first ballots of the 2012 presidential contest.

After weeks of face-to-face campaigning and millions of dollars in advertising, Republican presidential hopefuls made last-minute appeals to undecided GOP voters.

A confident Mitt Romney, the front-runner for the GOP nomination, told a rally Monday, "We're going to win this thing."

Whether he would pull that off was far from clear. The two who appear most likely to challenge Romney for the Iowa victory are former Pennsylvania Sen. Rick Santorum and Rep. Ron Paul of Texas.

More than a third of all potential caucus-goers say they could yet change their minds.

President Barack Obama is also thinking about Iowa today. The president will host a live web chat tonight with Iowa supporters, just as the caucuses are unfolding. Tomorrow, Obama will focus on the economy during a trip toCleveland, Ohio.