Front-running Democrat Hillary Clinton, a New York senator seeking to be the first female president, won an effusive welcome at a mainly black Baptist church in snowy Waterloo, Iowa, where she criticized the Bush administration for failing to expand health care coverage and alienating foreign allies.

"Do we take a leap of faith and once again bind the wounds of those who hurt, create a country that we're proud of, assume the leadership and moral authority of the world that we should or will we continue to just slowly but surely fall backwards?" she said, also touching on the upcoming Christmas holiday.

Religion plays a big role in politics in the United States, where levels of belief and church attendance are much higher than in Europe.

Other issues weighing on the minds of voters in the run-up to the November 2008 presidential election include health care, immigration, the war in Iraq and a mortgage crisis.

Clinton's main rival, Sen. Barack Obama, also toured Iowa, bolstered by a new poll showing him alongside her in New Hampshire -- another early contest in the state-by-state process to nominate both parties' candidates for president.

Republican hopeful Rudy Giuliani, a survivor of prostate cancer, returned to the campaign trail in New Hampshire after being hospitalized overnight last week with what he said was a "headache worse than I've ever had."

"I feel great now, I feel terrific. I've been tested out, everything came back 100 percent," Giuliani, a former New York mayor, said on ABC News' "This Week" program, adding his doctor would address the episode after Christmas.

"There's always the issue of cancer, so I'm going to have him put out a statement and then, you know, make everyone really comfortable that I'm OK."

Giuliani's battle with prostate cancer prompted him to drop out of the 2000 Senate race in New York against Clinton.

OBAMA SURGES, GIULIANI SLIPS

Giuliani, who plays heavily on his leadership in New York after the September 11 attacks in 2001, has led national polls of Republican voters but trails in New Hampshire and Iowa, which holds the nation's first nomination contest on January 3.

In New Hampshire's primary vote on January 8, Giuliani is fighting to keep up with former Massachusetts Gov. Mitt Romney and Sen. John McCain of Arizona.