(CNN) – Despite primary struggles with evangelical voters evidenced by losses in southern Bible Belt states, Mitt Romney has a large lead over President Barack Obama among white evangelical voters, a poll released Thursday showed.
The Public Religion Research Institute poll showed Obama carrying Catholic and mainline Protestant voters, as well as voters who did not identify a particular denomination.
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Romney's lead among white evangelicals was nearly 50 percentage points, as 68% chose him and 19% chose Obama in the survey.
In several Bible Belt primary states, Romney, a member of the Church of Jesus Christ of Latter-day Saints, stumbled among evangelical voters, who split their support for Rick Santorum and Newt Gingrich, both Catholics. Santorum was known for the central place social issues took on his platform and in his campaign pitches.
Over half of those surveyed said it was not "important for a presidential candidate to share their religious beliefs," but two in three white evangelical voters said shared beliefs were important or very important.
Although voters overall downplay the importance of religion in their candidate choices, the survey's authors pointed to a "strong correlation between similarity of candidates' religious beliefs and voting preference." Each candidate leads among voters who believe the other candidate's religious views are different from her own.
An exception to that is among the white evangelicals surveyed: 67% of those who said that Romney's Mormon faith is different from their own still supported him over Obama.
Romney will have an opportunity to address the gap this Saturday, when he delivers the commencement address at the evangelical Liberty University.
Obama's Wednesday announcement that he supports same-sex marriage could deepen the evangelical disapproval of Obama, who had originally expressed opposition to marriage, but supported same-sex unions. "I was sensitive to the fact that - for a lot of people - that the word marriage is something that provokes very powerful traditions and religious beliefs," he said in the Wednesday announcement.
The poll was completed prior to Obama's announcement, but included interviews conducted on the day when Vice President Joe Biden said he favored same-sex marriage.
The issue may not matter among voters overall, though, as polls show it holding low importance to the electorate, which is nearly evenly split on the issue.
Obama's advantage among Catholic and Protestant voters was less pronounced than Romney's lead among evangelical voters. Obama carried Catholics 46% to 39% and mainline Protestants 50% to 37%, the survey said.
It showed him having a larger advantage among those who did not identify with a denomination, by a 57% to 22% margin.
The PRRI pollster, Robert Jones, said the evangelical vote may be out of Obama's reach.
“The evangelical community has been tough for Democrats for recent history," he said. "They supported McCain, they supported Bush – they are heavily Republican leaning. It is a tough rode for any democratic candidate.”
As the GOP transitioned from primary to general election focus, some social conservatives and evangelical leaders moved to embrace Romney and dispel questions about his faith, such as prominent pastor Joel Osteen, who told CNN's Wolf Blitzer in April, "Mormonism is a little different, but I still see them as brothers in Christ."
The endorsement of former rival Republican candidates Santorum and Minnesota Rep. Michele Bachmann may also help Romney to shore up the demographic.
Others, like Southern Baptist Convention public policy chief Richard Land, have pointed to Romney's faith as a liability in the general election.
But despite these discussions of the candidates' faith, the survey shows voters' knowledge of Obama and Romney's religion is largely unchanged since an October poll. Just over a third of voters identify Obama as a Protestant, and 51% of voters identify Romney as Mormon.
The survey was conducted with 1,006 people by phone between May 2 and May 6, with a sampling error of no more than plus or minus 3.8 percentage points.
– CNN's Dan Merica contributed to this report