"I know a lot of people who will support him just because he's a Mormon — and I know a lot of other people who are edgy about that," said Paul Starita, a Minnesota native attending the church-owned Brigham Young University in Provo.

Many Mormons backing Romney recognize the risks but say it would be wrong to suppress their solidarity. Heather Johnson, a mother of three transplanted from Utah to North Carolina, started a "Moms4Mitt" Web site and hopes to campaign for him in South Carolina, a key early state in the primary process. That will be possible, she notes, only because her LDS "brothers and sisters" will put her up, and help watch her kids, wherever she goes.

"You cannot deny that there is a network in the church, a natural network," she said. "Some people make out like it's a conspiracy, but it's a natural networking system. It's just the way our church is set up."

The dilemma faced by Romney and members of The Church of Jesus Christ of Latter-day Saints recalls in some ways what John F. Kennedy faced running as a Roman Catholic in 1960. Among the factors that make this situation different, say political scientists, is that Mormons are almost unmatched in their cohesiveness and capacity for unified action.

Campaign spokesman Kevin Madden said Romney welcomes the backing he is receiving from Mormons, which he compared to the help that other candidates have received from their ethnic or religious roots, such as Michael Dukakis' support from fellow Greek-Americans in 1988. But Madden said Mormon support makes up only one element of Romney's base.

"We are happy of and proud of all the support we have received from members of the LDS. A lot of these supporters are interested in helping the governor because they think he would make a great president," Madden said. But, he added, "if we're going to win, it's going to require a broad spectrum of the American people."

A breakdown of the donors who gave the $21 million — $6 million more than former New York mayor Rudolph W. Giuliani, his nearest competitor — will not be available for more than a week. And Romney's political action committees, which have accumulated $8 million since 2004, have received substantial amounts from non-Mormons such as former colleagues in Boston finance circles, friends and associates in Michigan, where he grew up, and from business executives such as eBay chief executive Meg Whitman and Compuware founder Peter Karmanos.