Recent polls by Gallup, Pew and the Washington Post/ABC News have found increasing public support over the years for gay marriage in principle. The Post/ABC poll found 53 percent of Americans said gay marriage should be legal. As recently as six years ago, that figure was 36 percent.
The poll also found 71 percent of the 1,004 adults polled say they have a friend, family member or acquaintance who's gay.
But the tide of legal action in the states has been for voters to pass constitutional amendments barring such marriages. Most recently, North Carolina May 8 passed such an amendment by 61 percent of the vote.
Six states and the District of Columbia allow same-sex couples to marry. Thirty states have constitutional amendments banning same-sex marriage; some of those also prohibit civil unions and other approaches that grant legal rights to such couples. Twelve states permit civil unions.
Obama explained May 9 to ABC's Robin Roberts that he believes same-sex couples should be able to marry; that faith institutions should still get to determine what constitutes the sacrament of marriage; and that the issue will be worked out at the local or state level, not nationally.
The number of people who say Obama's remarks changed their opinion of him for better is about equal to the number who say his support has changed their opinion for the worse.
A May 10-13 poll by the Pew Research Center for the People & the Press found 52 percent of the 1,003 adults surveyed said Obama's expression of support for gay marriage did not affect their opinion of him. About a quarter said it made them think of him less favorably and 19 percent said they feel more favorably. The differences between the two are within the statistical margin of error of plus or minus 3.6 percentage points.
In the interview, Obama said he would like to see a national conversation on the issue continue in a respectful way.
People who feel strongly that marriage "should be defined narrowly as between a man and a woman, many of them are not coming at it from a mean-spirited perspective," Obama said. "They're coming at it because they care about families. ... They have a different understanding ... of what the word 'marriage' should mean." He added that many people with this view are his friends; others, such as pastors, are people whom he respects deeply.
On the other hand, Obama said, when he meets same-sex couples and their families -- including some people who work at the White House and the parents of some of his daughters' friends -- he hears from them "the pain they feel that somehow they are still considered less than full citizens when it comes to their legal rights. For me, I think it just has tipped the scales in that direction."
He added that it's important that efforts to legalize same-sex marriages are respectful of religious liberty. He said he thought that as it passed its law permitting same-sex marriage, New York "did a good job of engaging the religious community... making it absolutely clear that what we're talking about are civil marriages and civil laws."
Churches and other faith institutions "are still going to be able to make determinations about what their sacraments are -- what they recognize," Obama said. But from the perspective of the law, "I think it's important to say that in this country we've always been about fairness, and treating everybody as equals. Or at least that's been our aspiration."
The Catholic Church and many other faiths teach that marriage is a sacrament between one man and one woman. The U.S. Conference of Catholic Bishops is conducting a major campaign to oppose same-sex marriage and to instruct Catholics and the general public on the teaching.
As on most topics, U.S. Catholics poll much like the rest of the country on the issue. A Pew study in February found 52 percent of Catholics support allowing same-sex marriage.
Cardinal Timothy M. Dolan of New York, president of the U.S. bishops' conference, was among religious leaders who criticized Obama's position. He said the remarks were "deeply saddening," and that they "are not surprising since they follow upon various actions already taken by his administration that erode or ignore the unique meaning of marriage."
Grant Neeley, an associate political science professor at the University of Dayton in Ohio, told Catholic News Service in a May 23 phone interview that Obama's discussion of his position is unlikely to have a noticeable effect on voting in November.
Poll after poll shows that people vote primarily on issues such as the economy, with morality matters more likely to only shape a voter's overall opinion of a candidate, he said.
Obama's expression of support for gay marriage might motivate both strong supporters and strong opponents of such marriages to be active in the campaign, Neeley said, but it's probably not the single issue that will determine how many people vote.
Obama's discussion of same-sex marriage "was a personal policy statement," for one thing, Neeley said, and it's unclear what, if anything, the president might do to bring his views to bear on public policy.
Nor is it obvious what the likely Republican candidate for president, former Massachusetts Gov. Mitt Romney, could do in office to carry out his opposition to same-sex marriage, Neeley said.
Obama previously announced his belief that the Defense of Marriage Act, a 1996 law that declares marriage is between one man and one woman, is unconstitutional. He said that though the administration would continue to enforce the law, it would not defend it in court. But Neeley said it's unlikely in the current political climate that Congress would seriously attempt to overturn the law.
"I'm not sure this changes the political landscape at all," Neeley said. "It merely shifts the debate somewhat."