Obama supports gay marriage: How will it affect his re-election campaign?

— -- President Barack Obama's history-making embrace of gay marriage could send far-reaching political aftershocks through a presidential campaign defined by voter concerns about the economy but likely decided by slivers of the electorate in a handful of battleground states.

"The politics, it's not clear how they cut in some places that are going to be pretty important in this electoral map. It may hurt me," Obama told Robin Roberts of ABC News in an exclusive interview Wednesday as he announced his change of heart.

A Democratic senator who supports Obama's re-election as well as gay marriage told Yahoo News that the president could face "significant electoral risk" if his announcement is merely a check-the-box exercise with no follow-through.

"If the president simply makes an important commitment to equality and moves on, and does not challenge the network of people nationally, activists and others, who favor marriage equality, to speak up from now through the election, he is taking a significant electoral risk," said the senator, who spoke on the condition that he not be identified by name.

"When you move from 'civil union' to the word 'marriage,' it reaches people differently," the senator said in a telephone interview, warning that highly motivated foes of gay marriage will unleash a campaign of "public speeches, sermons, newsletters, websites, that will darkly suggest a negative future."

Obama echoed that sentiment, telling ABC News: "I had hesitated on gay marriage in part because I thought civil unions would be sufficient, that that was something that would give people hospital visitation rights and other elements that we take for granted and and I was sensitive to the fact that for a lot of people, you know, the word marriage was something that evokes very powerful traditions, religious beliefs, and so forth."

Richard Socarides, a leading gay activist who served as President Bill Clinton's top adviser on issues like same-sex marriage, said Obama "can help build a national consensus."

"Nobody expects the president to make this a central feature of his presidency, but it is an important issue," Socarides told Yahoo News by telephone.

Other Obama supporters pointed to a Gallup national poll, released Tuesday, showing that the country has been "evolving" on the issue along with the president.

The public opposed gay marriage by a lopsided margin of 68 percent to 27 percent when Gallup first asked the question in 1996. In 2012, for just the second year, a narrow majority of 50 percent favored making it legal, with 48 percent against. (The margin of error was plus or minus 3 percentage points.) Independent voters were strongly in favor, 57 percent to 40 percent, which on the surface would seem to help the embattled incumbent.

In what both sides expect to be a hotly contested election, the outcome could turn on relatively few voters in up-for-grabs states--like North Carolina, which voted 61 percent to 39 percent Tuesday to adopt a constitutional amendment banning gay marriage and civil unions. Obama beat John McCain there by just 13,692 ballots in 2008, and he leads Mitt Romney by 2.4 percentage points according to a Real Clear Politics average of polls.

"It was important for me, given how much attention this issue was getting--both here in Washington but elsewhere--for me to go ahead, let's be clear, here's what I believe," Obama told ABC News.

"But I'm not going to be spending most of my time talking about this, because frankly my job as president right now, my biggest priority, is to make sure that we're growing the economy, that we're putting people back to work, that we're managing the draw-down in Afghanistan effectively," he said. "Those are the things that I'm going to focus on."

One in six of the Obama campaign's "bundlers"--who corral big money donors--is gay, according to The Washington Post.

Hours before the interview, Mitt Romney and his campaign were keeping their powder dry. Aides did not respond to requests for comment, and the presumptive Republican nominee himself shook off a question as he shook hands after a campaign event near Denver. "Not on the ropeline," Romney replied, when Politico's Reid Epstein asked him if he had any comment on the "president and gay marriage."

Romney did address the topic of same-sex marriage during a television interview Wednesday in Denver. Asked by Fox affiliate KDVR-TV about a bill that would have allowed civil unions for same-sex couples in Colorado, Romney reiterated his belief that marriage is between a man and a woman.

"Well, when these issues were raised in my state of Massachusetts, I indicated my view, which is I do not favor marriage between people of the same gender, and I do not favor civil unions if they are identical to marriage other than by name," Romney said. "My view is the domestic partnership benefits, hospital visitation rights, and the like are appropriate but that the others are not."

A Romney spokeswoman did not respond to a request to clarify what Romney meant by "others."

There is little evidence to support the oft-repeated claim that coming out in favor of gay marriage will cost Obama much support among black voters.

But political analysts also point to working-class, white, religious voters in pivotal states like Ohio and Pennsylvania, and conservative-leaning independents in other important states like Iowa and Nevada as potentially put off by Obama's new position.

"African-American voters, who tend to be less sympathetic to gay marriage than white voters, are very enthused about Obama and, I think, this won't change that," said Ohio State University political science professor Paul Allen Beck .

"But the question in places like Ohio will be how this affects blue-collar white voters who might otherwise be predisposed to vote Democratic. For some of them, particularly the ones who are more deeply religious, this could be important," Beck told Yahoo News.

"For almost all Americans, this won't be directly a factor in November. But elections are won and lost at the margins, especially in Ohio," Beck said.

Pennsylvania Democratic Sen. Bob Casey's reelection fight highlights the difficult balancing act for politicians in swing states. Casey opposes gay marriage but favors allowing civil unions. His Republican opponent, Tom Smith, would favor a constitutional amendment defining marriage as between a man and a woman, but would not support a ban on civil unions, Smith's campaign manager Jim Conroy told Yahoo News by telephone.

But the Obama campaign may have calculated that the president's waffling--it could no longer be dubbed "Clintonian" after Bill Clinton actively campaigned against the North Carolina amendment--would tarnish his "hope and change" brand and dampen enthusiasm among liberal Democrats, young voters and single women, all key parts of his winning coalition in 2008.

"They ripped off the Band-Aid, didn't they?" a Democratic congressional aide told Yahoo News, saying that Vice President Joe Biden's endorsement of same-sex marriage on "Meet The Press" Sunday had forced the White House to confront "head-on" an issue they had hoped not to take up.

In 1996, Obama said on a campaign questionnaire in Illinois, "I favor legalizing same-sex marriages, and would fight efforts to prohibit such marriages." White House Communications Director Dan Pfeiffer later disavowed that statement, saying "someone else, not the president" had filled it out.

As president, Obama signed a law repealing the "Don't Ask, Don't Tell" ban on openly gay servicemembers, and ordered his administration to stop defending in court the Defense of Marriage Act, which prohibits the federal government from recognizing same-sex unions.

"My feelings about this are constantly evolving," Obama told reporters at a press conference one month after Republicans romped in the November 2010 mid-term elections.

"I struggle with this. I have friends, I have people who work for me, who are in powerful, strong, long-lasting gay or lesbian unions. And they are extraordinary people, and this is something that means a lot to them and they care deeply about," Obama said.

He went on to say: "At this point, what I've said is, is that my baseline is a strong civil union that provides them the protections and the legal rights that married couples have.  And I think--and I think that's the right thing to do.  But I recognize that from their perspective it is not enough, and I think is something that we're going to continue to debate and I personally am going to continue to wrestle with going forward."

People in Ohio have been "evolving" on the issue, too, said Beck, the political scientist. Ohio "public opinion probably has changed, as it has nationally," he said.

But "how much it has changed, I don't know."

Holly Bailey contributed reporting.