President Obama's decision to publicly support same-sex marriage may have changed the minds of some Americans, according to a national poll. But in states that will vote on the issue in November, the impact has been mixed.

Gay-marriage advocates say they have raised more money and attracted additional campaign volunteers since the president's historic announcement in May. But opponents downplay Obama's potential impact, beyond serving to mobilize their conservative base.

Four states will ask voters to weigh in on same-sex marriage, with the possibility that it could be upheld as law in Maryland, Maine and Washington state. In the fourth state, Minnesota, where gay marriage already has been outlawed, voters will consider a constitutional amendment to ban it.

Most polling has shown a majority of Americans have come to support gay marriage, but the issue has failed at the ballot box every time. In the 32 states in which voters have had a say, they have rejected it. In the six states and Washington, D.C., where same-sex marriage is legal, it came through legislative or court action.

As the first president to endorse same-sex marriage, Obama does so while the issue remains divisive and politically risky for him. To gauge the potential impact of Obama's decision, some historians compare it to President Kennedy's 1963 speech in which he stood up for civil rights as "a moral issue" or President Lincoln's opposition to slavery. Kennedy's approval rating dropped to its worst low, and Lincoln was met with the Civil War.

"The short-run political costs can be devastating," says Barbara Perry, a presidential scholar at the University of Virginia's Miller Center. "But we want our presidents to lead, right? If a president can put aside politics and make these kinds of decisions for moral reasons — and if they can stay the course— history regards them well."

Obama's Impact On Maryland Voters

In Maryland, where voters will decide whether to uphold a same-sex law passed this year, opponents and supporters alike say that Obama has significantly influenced the debate.

In March, a Public Policy Polling sampling of Maryland voters showed 52 percent said they would uphold the new law in November, and 44 percent said they would repeal it.

Two weeks after Obama's announcement, PPP found support had climbed to 57 percent and opposition had dropped to 37 percent. The 12-point swing was driven by African-Americans, whose support for the law jumped to 55 percent, up from 39 percent in March.

The size of the shift was unexpected because blacks in other states have consistently voted against gay marriage, citing deeply held religious objections to homosexuality. Black voters hold considerable influence in Maryland, where they made up a quarter of the electorate in 2008.

"The African-American community supports the president very strongly, and for the president to take a stand on the issue was something we think is going to be important in helping other African-Americans come around," says Josh Levin, campaign manager for Marylanders for Marriage Equality, which is working to preserve the law.

The campaign says it has attracted about 6,500 new volunteers in the past month and received three times more donations than in April and May combined. (The campaign declined to provide actual figures.)

Derek McCoy, executive director of Maryland Marriage Alliance, said Obama's position also helped fuel his group's signature drive, which forced the referendum.

"What it has done is energize people to uphold what has been the definition of marriage," McCoy says. "What he's also done is stir up a lot of people in the Democratic Party to say 'Enough is enough. I'm drawing the line on this issue.' "

'A Culturally Defining Issue'

In Washington state, the new same-sex marriage law was scheduled to take effect June 7. But the day before, opponents submitted enough signatures to force a referendum.

Joseph Backholm, the chairman of Preserve Marriage Washington, which opposes gay marriage and collected the signatures for the referendum, says "it's beyond dispute at this point that polling on the issue of gay marriage is totally unreliable."

Backholm predicts Obama's announcement "will ultimately be of no consequence," although he says it did initially trigger "a slight uptick" in donations to the campaign and a "dramatic increase" in volunteers gathering signatures. The group has raised roughly $105,000, Backholm says.

"There are a lot of people who have never been involved in a political issue that are now getting involved because they understand the significance of this as a culturally defining issue," Backholm says, adding that more than 1,500 churches have signed on.

The leading gay-marriage proponent, Washington United for Marriage, on Monday said June fundraising delivered its highest monthly sum, $952,267. A pair of $100,000 donations came from Microsoft co-founder Bill Gates and current Chief Executive Steve Ballmer, bringing total donations to more than $2 million, according to campaign manager Zach Silk.

Silk said it helped that Obama visited the state on the day after his announcement. And, he said, Gay Pride Month celebrations in June raised the intensity of supporters. Also in June, a Public Policy Polling survey found that for the first time in a year of sampling, a slight majority of Washington state voters favored the legalization of gay marriage.

"I think there's a feeling in the country and here in Washington that we're at tipping point on this issue," says Silk.

Maine Voters Prepare For Rematch

With this year's initiative, Maine becomes the first state in which supporters of same-sex marriage, rather than opponents, have put the issue on the ballot. Voters in 2009 overturned a law passed by the state Legislature, but supporters never stopped organizing.

"We haven't seen much of an effect in our polling, nor would I expect that to be the case," says Matt McTighe, campaign manager for Mainers United for Marriage, a coalition of groups advocating gay marriage. "This is just such a personal issue that it's something people here can only come to support on their own terms."

Carroll Conley Jr. is executive director of the Christian Civic League of Maine and a board member of Protect Marriage Maine, which leads the opposition. He says, "Of course it makes a difference if the president of the United States comes down on any issue. There's no doubt it created dialogue." But, Conley says, he's seen no noticeable shift in voter opinions.

McTighe says organizers "meet people where they are" and have had personal conversations with more than 100,000 voters, targeting those who are undecided. He says 2012 was chosen to try to take advantage of the usually larger turnout for presidential elections, which attract more young voters who tend to support gay marriage.

A June poll by NPR member station WBUR and the MassINC Polling Group found 55 percent of Maine voters favored a law that would provide marriage licenses to same-sex couples but exempt religious institutions from being required to perform the nuptials. Thirty-six percent opposed it and 9 percent were undecided or refused to answer.

Opponents are relying heavily on turning out church congregations and on fundraising help from the National Organization for Marriage. Conley says he expects to be outspent by the same-sex marriage campaign, which he believes carries the "weight of changing people's minds."

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