Senator Kirsten E. Gillibrand, Democrat of New York, called the president’s statement “a watershed moment in American history” that would aid efforts to overturn the Defense of Marriage Act barring federal recognition of same-sex marriage.
Mayor Michael R. Bloomberg of New York said, “No American president has ever supported a major expansion of civil rights that has not ultimately been adopted by the American people, and I have no doubt that this will be no exception.”
Some supporters saw the president’s announcement in more political terms.
“For thousands of supporters who donated, canvassed and phone-banked to help elect Barack Obama in 2008, this is a powerful reminder of why we felt so passionately about this president in the first place,” said Michael Keegan, president of People for the American Way, a liberal interest group.
“I’m almost in tears,” said Steve Clemons, director of the American Strategy Program at the New America Foundation, a nonpartisan research group. Mr. Clemons, who is gay and was married in California in 2008, said the announcement would ignite progressives at a time when there was some ambivalence on the Democratic left as to how forcefully to support Mr. Obama’s re-election bid.
Mr. Clemons compared that ambivalence to that of evangelicals on the Republican right toward Mr. Romney. But now, in one single step, Mr. Obama, at least, has erased any ambivalence his base might feel toward his candidacy, Mr. Clemons said.
Opponents of same-sex marriage said, however, that the president’s position would hurt him in November.
“Considering that 10 of the 16 battleground states have marriage amendments that could be overturned by the president’s new policy position on marriage, today’s announcement almost ensures that marriage will again be a major issue in the presidential election,” Tony Perkins, the president of the conservative Family Research Council, said in a statement.
Gary Bauer, president of American Values, a conservative organization that opposes same-sex marriage, faulted Mr. Obama for diverting his attention from the economy.
“Every American who can’t find work, whose home is under water or who can’t afford to fill up his gas tank should be wondering why the president is spending even one second of his time thinking about how to radically transform the institution of marriage,” Mr. Bauer said in a statement. “It’s a political move meant to energize his left-wing base and distract Americans from his disastrous economic policies.”
Mr. Obama’s comments came in an interview with ABC News’s Robin Roberts that was arranged by the White House, knowing that Ms. Roberts is a popular correspondent, well-known especially among female viewers as a cancer survivor and among African-Americans, a group in which there is widespread opposition to same-sex marriage.
The interview was intended to be wide-ranging, but it inadvertently became the outlet for Mr. Obama’s long-awaited evolution on same-sex marriage in a week that began with the remarks of his vice president, Joseph R. Biden Jr., all but embracing same-sex marriage in an expansive answer to a question on NBC’s “Meet the Press” on Sunday.
Mr. Biden’s well-publicized comments increased the pressure on Mr. Obama to take a stand, with his press secretary, Jay Carney, pummeled with questions from White House reporters. Newspaper editorials, columnists and bloggers assailed the president’s ambivalence, demanding clarity before the election. On Tuesday, Mr. Carney signaled that Mr. Obama would soon address the matter.
But the timing was forced on the president in other ways.
On Thursday, Mr. Obama is to attend a fund-raiser in Los Angeles at the home of the actor George Clooney, which is expected to raise about $12 million, much of it from Hollywood people active in the gay-rights cause. On Monday, Mr. Obama is scheduled to speak at a campaign fund-raiser and reception of the Lesbian, Gay, Bisexual and Transgender Leadership Council in New York City, where the special guest is Ricky Martin, the singer who is gay. On June 6 Mr. Obama is scheduled to return to Los Angeles to speak at a gala benefiting the gay, bisexual and transgender community, with tickets costing up to $25,000. And this summer, Democrats will begin meeting to draft the party’s platform for the national convention that will nominate Mr. Obama in September, and some gay-rights activists are pushing to include language endorsing same-sex marriage. The president and his advisers in the White House and at the campaign headquarters in Chicago knew Mr. Obama would repeatedly have to parry questions and criticisms on the issue. That prospect, several Democrats said, suggested that the greater political risk for Mr. Obama was not in coming out for same-sex unions but in appearing to be politically calculating, especially given that most supporters believe he personally has favored same-sex unions.
“He’s been on this evolution since November 2010, and it’s been getting kind of awkward,” said Fred Sainz, a spokesman for the Human Rights Campaign. “The word evolution signifies change that has an ending at some point.”