Eric Gay, Associated Press
Supporters of Republican presidential candidate, former Massachusetts Gov. Mitt Romney listen during a campaign stop, Saturday, Dec. 31, 2011, in Le Mars, Iowa.

LE MARS, Iowa — The Republican presidential race in Iowa is coming down to which way an enormous number of undecided voters breaks in the coming days.

With the caucuses looming Tuesday, Mitt Romney is contending for victory in a state that eluded him four years ago.

Rick Santorum — a favorite of social conservatives — is surging. Ron Paul and Newt Gingrich appear to be losing ground. Surveys show Rick Perry and Michele Bachmann trailing.

But the dynamics can shift rapidly.

Underscoring the unpredictability of the race, a new poll by The Des Moines Register finds that a remarkable 41 percent of likely caucus-goers say they're undecided or still might change their minds.