(CNN) -- Democrats have usually conceded the evangelical vote during presidential elections, but Sen. Barack Obama is trying to change that by mobilizing what some call the "Christian left."
Sen. Barack Obama is expected to talk about faith-based initiatives during a campaign stop in Ohio on Tuesday.
As part of his outreach to evangelical voters, the presumptive Democratic presidential nominee will tour the Eastside Community Ministry in Zanesville, Ohio, on Tuesday and give an address on how he plans to builda "real" partnership between faith-based organizations and the White House if he becomes president.
Obama's outreach to evangelical voters has also included private summits with pastors, an effort to reach out to young evangelicals and a fundraiser with the Matthew 25 political action committee. It describes itself as a group of moderate evangelicals, Catholics and Protestants committed to electing the Illinois Democrat president.
Matthew 25's name is inspired by a biblical passage, in the 25th chapter of the Gospel of Matthew, in which Jesus says, "For I was hungry and you gave me food, I was thirsty and you gave me drink." The name is meant to signal the group's focus on social justice concerns about hot-button cultural issues.
Brian McLaren, a former pastor who spent 24 years in the pulpit and is now an informal adviser to the Obama campaign, believes that a significant portion of evangelical voters are ready to break from their traditional home in the the Republican Party and take a new leap of faith with Obama.
"I think there's a very, very sizable percentage -- I think between a third and half -- of evangelicals, especially younger [evangelicals], who are very open to somebody with a new vision," McLaren said. Watch how young evangelicals are entering politics »
That new vision, he said, isn't focused on traditional social issues like abortion and gay marriage but more on efforts to end global warming and the war in Iraq.
"We've watched the evangelical community be led -- be misled -- by the Republican Party to support things they really shouldn't have supported," McLaren said, including "the blind support for the Iraq war when it was launched on either mistaken or false pretenses."
Unlike previous presidential elections, when the religious right's criticism of Democratic presidential candidates went largely unchallenged, Obama's evangelical supporters rallied around the Democrat when Christian conservative James Dobson accused him of "deliberately distorting the traditional understanding of the Bible."
Pastor Kirbyjon Caldwell, the Texas minister who officiated at first daughter Jenna Bush's wedding, and "a coalition of pastors and other Christians ... who are standing up for our Christian faith and supporting Barack Obama" created a Web site called "James Dobson Doesn't Speak For Me" that attempts to refute Dobson's claims with quotes from Obama.
"The Apostle John speaks for me in reminding us of Jesus' command to love one another. The world will know His disciples by that love," a statement on the site says. "These words speak for me. But when James Dobson attacks Barack Obama, James Dobson doesn't speak for me."
Recent polling suggests, however, that a majority of white evangelical voters are still backing Sen. John McCain, though enthusiasm for the presumptive Republican presidential nominee among evangelicals is less than what it was for President Bush in 2004. Watch McCain fight for the evangelical vote »
In a CNN poll conducted by Opinion Research Corporation on June 4-5, nearly two-thirds of white evangelical voters surveyed, 64 percent, supported McCain, and 30 percent backed Obama. The poll's margin of error was plus or minus 6.5 percentage points.
In comparison, Bush received the support of 78 percent of evangelical voters in the 2004 election, according to exit polls.
Despite the lower enthusiasm for McCain among rank-and-file evangelicals, leaders of the Christian right movement have already attacked Obama for his social views. In one instance, Tony Perkins, president of the Family Research Council, posted a video on YouTube that challenged Obama's position on abortion.
"Talking about faith issues is not about singing 'Kum Ba Yah,' " said Charmaine Yoest of the Family Research Council, another conservative evangelical group. "It's about the public policies the person is going to put in place."
But some leaders of the religious right who worked hard to get Bush into the White House have been underwhelmed by the outreach from the McCain campaign and are less likely to fight for McCain as they did for Bush.
For example, in spring 2004, Michael Farris and his organization, Generation Joshua, were heavily involved in the planning for a fall effort to drive evangelical voters to the polls to re-elect Bush.
But Harris and his organization had yet to be contacted by the Republican National Committee or McCain's campaign as of mid-June and did not plan any efforts in key swing states as they did in 2004.
"We don't feel invested in his candidacy," Farris said, "and he clearly doesn't feel invested in us."
Farris is not alone among evangelical leaders about his uneasiness with McCain.
"The evangelical community seems to be sitting on the fence to a particular degree," said Jacques Berlinerblau, a professor at Georgetown University.
And that could give Obama an opportunity, he said.
"If Sen. Obama can get between 30 and 33 percent [of the evangelical vote] in those crucial swing states, he's absolutely golden," Berlinerblau said.
CNN's Jim Acosta and Rebecca Sinderbrand contributed to this report.