U.S. Republican presidential candidates are preparing for their last debate before the start of the national nominating process in Iowa next month.

The candidates will debate later Thursday in Iowa as they vie for a chance to unseat President Barack Obama, a Democrat, in the 2012 election.

The Republican nominating process begins in the Iowa caucuses on January 3.

Opinion polls show the former speaker of the U.S. House of Representatives, Newt Gingrich, has surged ahead of former Massachusetts Governor Mitt Romney in the Republican race.

Gingrich leads the Republican nominees nationally and in three key early voting states — Iowa, South Carolina and Florida. He was at the bottom among Republican candidates a few months ago.

Texas Congressman Ron Paul, a libertarian, has also been gaining ground in the Republican race.

Rounding out the Republican field are Texas Governor Rick Perry, Minnesota Congresswoman Michele Bachmann, former Pennsylvania Senator Rick Santorum and former Utah Governor Jon Huntsman, once Mr. Obama's ambassador to China.

This week, a Wall Street Journal/NBC News survey of likely Republican voters put Gingrich 17 points ahead of Romney.

Separately, a poll released Wednesday showed that negative views of Mr. Obama have hit an all-time high. But the ABC News/Washington Post poll also found that Mr. Obama is viewed more positively than Gingrich.

Gingrich's unfavorable rating was 48 percent, but his favorable rating was 13 points lower than Mr. Obama's at 35 percent.