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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.

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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.