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John Kerry (search) is only the third Catholic candidate this close to getting all the way to the White House, but whether he can win over the Catholic vote in November could depend on his skill in separating his religious and political beliefs.

"He's in opposition to the Catholic Church on essential church teaching. He has the most radical stand one could have on the subject [of abortion]," said William Donahue, president of the Catholic League (search). "There's a serious question here that he's so out of sync with the church's teachings on the life issues that it's going to be a problem."

"To ask each communicant if they are pro-choice or pro-life is impractical," said former California gubernatorial candidate Bill Simon, who argued that Kerry should not be judged by his faith any more than any other individual.

Kerry's Web site touts the presumptive Democratic candidate as a committed adherent to the Catholic faith, similar to earlier Democratic nominees John F. Kennedy in 1960 and Alfred E. Smith in 1928.

"John Kerry was raised in the Catholic faith and continues to be an active member of the Catholic church," it reads.

The Massachusetts senator agrees with the church on social justice issues, including immigration, poverty, health care and the death penalty, and he did seek an annulment from the church after his first marriage. But Kerry holds different opinions from church doctrine on such issues as abortion and same-sex unions, both of which he supports.

Kerry has argued that he is a politician and not a cleric, and should be judged not on his adherence to his faith, but on his commitment to the U.S. Constitution (search). But whether or not his faith matters remains to be seen.

Catholics, who are 65-million strong in the United States, make up one-fourth of the electorate and traditionally lean Democratic. Republicans have chipped away at that advantage over the years. No presidential candidate since 1980, save Al Gore in the 2000 race, has won the Catholic vote and lost the White House.

But Catholic Democrats disproportionately backed Kerry over his opponents during primary season, and a Fox News-Opinion Dynamics poll taken earlier this week shows that of 269 registered Catholic voters polled, 47 percent supported Kerry while 41 percent preferred President Bush. Catholics also have a favorability rating of Kerry of 48 percent, while the general public has a rate of 43 percent. The margin of error was 6 percent.

The numbers have led some analysts to question whether Kerry's departures from Catholic doctrine will have any impact at all.

"The church can make its own rules, but it is also between the person and God," said radio talk show host and Fox News contributor Ellen Ratner.

"I'd like to think that religion is not a big factor these days. I think people will say whatever religion he has, that’s his," said Rev. Robert F. Drinan, a Catholic priest and former Democratic congressman from Massachusetts.

Drinan, now a professor at Georgetown University Law Center, said Kerry's faith may even help pick up Catholic Republicans, adding that a GOP attack on Kerry's observance "could boomerang badly."

While Kerry does not adhere to all the strictures of the faith, Bush may not be any better a choice for Catholics, added Mary Ann Walsh, spokeswoman for the U.S. Conference of Catholic Bishops (search).

"There is no candidate that is in agreement with the church on all issues," she said.

Still, church decisions could play a central role in swaying Catholic voters. In January 2003, prompted by international debate on stem cell research and human cloning, the Vatican released a "doctrinal note." Among other things, it said that "a well-formed Christian conscience does not permit one to vote for a political program or an individual law which contradicts the fundamental contents of faith and morals."

In February, Archbishop Raymond Burke (search) of St. Louis advised Kerry not to "present himself for communion" at any church in the city. Earlier in the year, Burke had cited support for abortion and euthanasia as issues he could not reconcile with political candidates.

In Kerry's Boston diocese, Archbishop Sean O'Malley has instructed Catholic politicians who back abortion rights to abstain from communion (search). But, unlike Burke, O'Malley has not suggested that priests refuse communion if politicians like Kerry present themselves. Kerry is expected to receive the sacrament on Easter Sunday at his church in Boston.

Donahue said that not only will many Catholics reject Kerry's commitment to his religion, but he may also expect a backlash among non-Catholics.

"One more time, is he speaking out of both sides of his mouth? It's adding to the profile that he seems to be everything to everybody. That is something he is going to have to answer when it comes to the subject of religion," he said.

"It's not going to be whether there's an animus against Catholics, but is he a Catholic in good standing," Donahue said.

Added American Enterprise Institute (search) Research Associate John Fortier, questions of Kerry's faith demonstrate just how much the country has changed since 1960, when anti-Catholic bias arose in questions about whether Kennedy would be more committed to his church than his state.

"The fact that really very few people have even noticed [Kerry's religion] shows that we're largely beyond it. I don’t think were going to face much talk about whether his loyalty is to the U.S. or the pope as we did with Kennedy," Fortier said.