But the Third Ward congregants don't seem inclined to hold a grudge.
"I hope he doesn't end up making that move ⅛to the White House⅜, but if he does, I'd welcome him with open arms," said Corban Tillemann-Dick, 26, who works phone banks for Obama's re-election.
In fact, if Romney wins, Tillemann-Dick hopes he might be picked to be the new president's "home teacher," a designated person every Mormon has in their congregation as a go-to caregiver.
"If he needed a friend to talk to or a shoulder to cry on - I think it would be a wonderful opportunity," he said.
A Romney campaign adviser said the Republican nominee, a devout former bishop, hasn't made any decisions about his hypothetical D.C. spiritual life. But it's unusual in Mormonism for people to go outside their assigned ward.
A president in the pews would be dramatic, but the D.C. Third Ward, as it's called, is used to drama. More ethnically and economically diverse than the typical Mormon ward, its roughly 200 congregants have included deported immigrants, a teen shot dead in gang violence, refugees from African wars and youths who depend on the church for meals, tutoring for class and support to pay for Boy Scout camp.
"The standard ward is all middle class, and there is no one you can help. If you want to serve someone or help someone out, there are always people here you can help," said Kevin Linzau, 51, a telephone systems programmer who lives in the Washington neighborhood where he grew up.
The ward is known in the area for its unusual demographics and high-energy warmth. Up to half of the congregation is nonwhite, including a large, Spanish-speaking population and converts from French-speaking Africa. The ward includes openly gay leaders, not typical for a socially conservative faith. There are also many converts and missionaries.
Although the majority of Mormons lean Republican, most Washingtonians lean Democrat, and the D.C. Third Ward is no exception. Congregants describe rolling their eyes when Mormon tourists who drop in for services rave about the possibility of the GOP retaking the White House. People share jokes about the first Mormon president - a converted Barack Obama.
"People ⅛in D.C.⅜ for the Glenn Beck rally came in here, all excited, and we were like, 'Oh, we still love you,' " said Robin Lunt, a local lawyer. "I think the Romneys would be happy in our ward and definitely welcomed, but it would be very different."
The ward is by far the largest of the three Mormon congregations that meet in the city. It will become officially the flagship in the capital next month when it opens the first new Mormon church in the city since the 1930s. After seven years of fighting neighborhood opposition, the Mormons will have a building - or meeting house, in Mormon lingo - on 16th Street, a boulevard of dozens of houses of worship where church officials felt it was symbolically an important place for the young American faith to be. The street runs south and ends at the White House, potentially a direct shot on Sundays for a President Romney.
The building is a big deal. One of the faith's leaders, called an apostle, will speak at a dedication on Oct. 28. To help smooth the new building's segue into the neighborhood, local Mormons organized a major food drive with other nearby churches and will assemble 1,000 boxes of food this weekend.
The Washington area has the biggest Mormon population east of Denver. Church officials attribute this, in part, to the powerful cultural value of public service in Mormonism - including through the government.
At the D.C. Third Ward, the possibility of Romney in the pews has set off quite a bit of chatter. Several congregants said they were surprised by Romney's disparaging comments about the nearly half of Americans who don't pay federal taxes.
In the remarks at a fundraiser captured secretly on videotape and released by Mother Jones last week, Romney referred to "the 47 percent" as "people who will vote for the president no matter what . . . who are dependent upon government, who believe that they are victims, who believe the government has a responsibility to care for them, who believe that they are entitled to health care, to food, to housing, to you-name-it."
"It's hard for me to believe that that's who he is," Tillemann-Dick said. "He's a brilliant guy, and he's spent a good chunk of his life trying to serve. It's hard for me to believe that he doesn't know that for many people there's no safety net. . . . I think it would be great for Romney if he was president to come to the ward every Sunday and be reminded there are a lot of real good, hard-working people who still depend on the government for some help. . . . I hope it would influence his policy."
This would hardly be the first time Romney worshiped among a diverse group of Mormons. He was bishop and then stake president over the city of Boston and much of the surrounding region.
The possibility of a Republican president in the pew has raised other topics, too.
What if, for security reasons, Romney didn't join the church? What if he was excused due to being too busy? Since every Mormon is assigned a "calling" or volunteer job in their church, if he did join, what would his be?
The Romney hypothetical tests Mormons, who are hugely proud of the fact that they have no paid clergy and a system built around equalizing the powerful with the peon. Mormonism calls for most everyone to be a home teacher and to have one, and it's a source of great pride that politicians and chief executives teach Sunday school, tutor or serve in the nursery on Sundays. Senate Majority Leader Harry Reid, D-Nev., is a home teacher and a leader of the men's group at his Chevy Chase, Md., ward, said a regional church spokeswoman.
Debbie Marriott Harrison, spokeswoman for the stake that includes the Third Ward (Mormon regions are called stakes, like dioceses), said Romney would likely be excused from a calling, partially because he'd be too busy as president and partially because of security challenges.
A core Mormon rule is the need for a regularly updated credential, called a temple recommend, in order to go to Mormon temples for marriages and baptisms for the dead. The credential is given every couple years after an interview with your local bishop to make sure you are attending church and living a moral life.
Romney would be interviewed by Robert Nelson, a jolly, 56-year-old information tech manager who is the ward's bishop.
"If he's here four years, I'd see him at least once! I just can't imagine," said Nelson, chuckling.