U.S. Republican presidential hopefuls debated Thursday in the politically influential midwestern state of Iowa, where the national nominating process begins in less than three weeks.

Republican contenders used much of the two-hour debate to criticize Newt Gingrich, who has emerged as the front-runner heading into the final stretch of the primary campaign.

The former speaker of the House of Representatives defended his recent involvement with disgraced mortgage giant Freddie Mac. Gingrich has admitted to receiving $1.6 million from the government-backed company, but insists he did no political lobbying for them.

Former Massachusetts Governor Mitt Romney, an early favorite in the race, focused much of his attention on President Barack Obama. Romney accused Mr. Obama of having a foreign policy of appeasement, and criticized him for a weak response in trying to retrieve a drone that recently crashed in Iran.

Meanwhile, Texas Congressman Ron Paul, who has done well in recent Iowa opinion polls, used the debate to defend his controversial views on foreign policy. Paul, who has been deeply critical of U.S. military efforts, referred to the recently ended war in Iraq as “useless.”

Also participating in the debate were 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.

It was the final debate before the nominating process begins with the Iowa caucuses on January 3.

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.