DES MOINES, Iowa — Former House Speaker Newt Gingrich wept Friday as he recalled his late mother's end-of-life illnesses, a moment of poignancy in a notably negative Republican presidential Iowa caucus campaign with four unpredictable days yet to run.

"I do policy much easier than I do personal," Gingrich told an audience of women as he tried to regain his composure. The tears flowed as the former speaker was responding to questions about his mother from a pollster and longtime political ally.

Gingrich's emotional moment came as his rivals engaged in traditional campaign tactics, and as polls suggested large numbers of Iowa Republicans could change their minds before caucuses Tuesday night provide the first test of the 2012 campaign.

Former Massachusetts Gov. Mitt Romney sought to marginalize his closest pursuer in most polls, saying, "I don't think Ron Paul represents the mainstream of Republican thought with regards to issues, particularly in foreign policy."

There was no immediate response from Paul, a Texas congressman who opposes the use of military force to prevent Iran from acquiring nuclear weapons.

Former Pennsylvania Sen. Rick Santorum, claiming momentum based on recent polls, told reporters he recently had the best fundraising day of his candidacy. Yet he also drew criticism from Texas Gov. Rick Perry for advocating earmarks during two terms in the Senate.

Minnesota Rep. Michele Bachmann became the latest presidential hopeful to hold a campaign event with Iowa Rep. Steve King — and the latest to hear him say he wasn't ready to give his endorsement.

Whatever the impact of Gingrich's tears on the race for the White House, the episode seemed destined to be replayed endlessly on televisions, personal computers and hand-held devices.

That was the case nearly four years ago, when Hillary Rodham Clinton appeared to choke back tears while campaigning in New Hampshire a few days before the state's Democratic presidential primary. The episode also became the subject of intense political analysis. Clinton won the primary in an upset a few days later.

Gingrich was surging in the polls a little more than a week ago, but was hit by a barrage of negative ads and has been struggling in recent days. Normally a combative politician, he shed tears as he appeared before a group of mothers and responded to a question from Frank Luntz, a Republican pollster and longtime ally of the former speaker.

Asked about his mother and an event in his life that influenced his policies and views, Gingrich recalled her as happy and having friends before she ended up in a long-term care facility suffering from bipolar disease, depression and physical ailments.

"My whole emphasis on brain science comes in directly from dealing with the real problems of real people," he said, his face distorting as he began to cry. "And so it's not a theory. It's, in fact, my mother," he said.

Kathleen "Kit" Gingrich died in 2003. She was 77.

Romney, who leads in most polls in Iowa, criticized Paul in an interview with Fox News Channel.

"I don't think Ron Paul represents the mainstream of Republican thought with regards to issues, particularly in foreign policy," he said, referring to the Texan's statement that he would oppose military action to prevent Iran from acquiring nuclear weapons.

At the same time he said Paul was outside the GOP mainstream, Romney pledged to support whoever wins the party's nomination to oppose President Barack Obama in the fall.

After months of campaigning and millions of dollars in television commercials, the polls depicted a race as unsettled and unpredictable as any in the four decades since Iowa's caucuses became the kickoff event in presidential campaigns.

A pair of surveys in the last five days suggested upwards of a third of all potential caucus-goers had not firmly settled on a candidate of choice.

The same polls made Romney the front-runner, and his decision to leave for a quick trip to New Hampshire and then return to Iowa and stay through caucus night projected optimism.

Paul views on Iran have been called into question this week by numerous other contenders, and Gingrich went so far as to say he would not vote for the Texan.

To some extent, Paul stands alone in the field because of his libertarian-leaning views. He does not want the government to have the power to ban abortions, for example, and has called for the legalization of some drugs that are now outlawed.

That has left Santorum, Gingrich, Perry and Bachmann to vie for standing as Romney's chief opponent in the competition for evangelical voters and other conservatives.

Even before the caucuses, Romney and the rest of the field were looking ahead to New Hampshire's primary on Jan. 10 and the first two Southern contests later in the month, in South Carolina and Florida.

Associated Press writers Thomas Beaumont and Kasie Hunt in Des Moines, Brian Bakst in Early and Mike Glover in Ames to this report.