Catholic voters are an important constituency in the battleground state of Ohio, where they represent about one-fourth of voters.
They went for President Bush in 2004, but for candidate Barack Obama in 2008. This year, for the first time, they'll be choosing between two tickets that both feature a practicing Catholic.
During last week's debate, GOP vice presidential candidate Paul Ryan spoke about his faith this way: "I don't see how a person can separate their public life from their private life or from their faith. Our faith informs us in everything we do. My faith informs me about how to take care of the vulnerable, about how to make sure that people have a chance in life."
His Democratic counterpart and fellow Catholic, Vice President Joe Biden, said his religion defines him.
"I've been a practicing Catholic my whole life. And it has particularly informed my social doctrine. Catholic social doctrine talks about taking care of those ... who can't take care of themselves."
Ryan stressed the church's teaching on life issues, such as abortion, while Biden stressed the social justice part of Catholic doctrine.
Vincent Miller, who teaches religion and theology at the University of Dayton in Ohio, says Biden and Ryan represent the two great themes in Catholics' politics.
"They care about life issues especially," he says. "Catholics also ... think in terms of community, and they think in terms of government having responsibility for community."
Miller says different issues bring out different Catholic voters. For instance, in 2004, there was a gay marriage amendment on the ballot.
"And there was very little people could do to affect their rather desperate situation on the economy, so votes gravitated toward that action that would let them do something," he says. "In this election, changes to Medicare are a real issue. The same communitarian — the same common good imagination that pushes them another way this time."
The division among Catholics can be seen at events held by a group called Nuns on the Bus. The nuns have been active and outspoken — and often at odds with the church's male-dominated hierarchy.
This fall, they're traveling around Ohio, calling attention to issues such as poverty.
Kathy Trangenstein of Oakwood, Ohio, came to see the Nuns on the Bus at a rally at the University of Dayton. She says she's still on fence about the election.
"I've always voted straight Republican," she says. "But now I see what's going on, and I'm afraid all the help is going to be cut off if the Republican ticket wins."
Meanwhile, Ellen Merkel of Centerville, Ohio, says abortion remains the key issue for her.
"The issue of life, we talk about it ... even the Republicans kind of give it lip service — but I'll support someone who at least gives me lip service more than I will on someone who says, 'I'm gonna double down on Planned Parenthood,' " she says.
Also on hand at the Dayton rally was Dottie Klein. She says she used to be a Goldwater Republican but now plans to vote for Obama, because she's looking for a different emphasis — "an emphasis on the poor."
"I think we need to help one another," she says. "I think that immigration is another thing — I think we're looking for scapegoats."
When the Nuns on the Bus reached Columbus, Greg Sutton was in the crowd. Sutton is an example of a Catholic voter moving away from the president.
"I did vote for this president, yes. I think actually it was the health care — the imposition of ... I don't like calling it Obamacare, but I don't know what else to call it," he says. "I think Obamacare started it, and then I became more disillusioned with the president."
Polls show the president fighting to defend a slim lead among Catholics in Ohio — a margin crucial to his fortunes in the state. The party that wins the Catholic vote in Ohio usually wins the state — and the winner in Ohio nearly always wins the election.