Republicans say they'll now use President Obama's stance on the issue -- public opinion is about evenly split -- to paint him as a flip-flopper and to boost Mitt Romney's image in the eyes of conservatives who are still warming to him.
Across the Republican Party, from leaders to activists interviewed since Obama's announcement, there's been wide agreement to use the gay marriage issue selectively. They want to use it in battleground states that have banned gay marriage, for example, while keeping the party's national political focus on Obama's stewardship of the economy.
"I'm going to stay focused on jobs, thanks," House Speaker John Boehner, a Republican, said repeatedly when asked about Obama's announcement on gay marriage. "The president can talk about it all he wants. I'm going to stay focused on what the American people want us to stay focused on."
Romney is taking a similar approach, avoiding any discussion of the issue unless he's questioned about it and focusing on the economy.
"It's hard right now. It's real tough," he said Friday in Charlotte, North Carolina. "It's because of the wrong policies. The right policies are going to put America back to work and make us the economic powerhouse we've always been."
While Republican activists acknowledge that the economy is the top concern for voters, they also see the night-and-day contrast between Obama and Romney on gay marriage as being too good not to exploit at the right times, in the right places. On questions of whether Romney's sufficiently conservative, for example. Or on the subject of consistency.
Particularly appealing, some activists said, was the White House's notion that Obama's "evolution" on the issue is somehow different from flip-flopping.
"This is one situation where Obama looks like the flip-flopper and Romney looks consistent," said Ralph Reed, president of the Faith & Freedom Coalition, a conservative, grass-roots advocacy group. "So much for the notion that Romney's the one with no core."
Romney has taken heat from Democrats and some Republicans for changing his position on some issues, such as abortion. But the former Massachusetts governor has not done so on gay marriage. He has been consistent in saying he believes marriage is between a man and a woman.
Obama held an identical position through his 2008 election, but he said in late 2010 that his views were "constantly evolving." Feeling pressured by events this week, Obama announced his new position Wednesday.
Before Obama went on record in support of same-sex marriage, Vice President Joe Biden last Sunday pronounced himself "absolutely comfortable" with men marrying men and women marrying women. Then on Monday, Education Secretary Arne Duncan said he supports gay marriage, too. The next day, voters in North Carolina approved a constitutional amendment banning gay nuptials, making it the 30th state to do so.
Besides the political and financial value of the issue, Republicans see a geographic benefit since several of the states that will decide the White House race have banned gay marriage in some form. In Ohio, Florida, Nevada and Virginia, for example, highlighting Obama's embrace of gay marriage and Romney's opposition to it could help energize conservative constituencies and win over right-leaning independents.
"This isn't going to be the No. 1 issue in the campaign, but it's going to mean a point or two in some of those selected states," said Richard Viguerie, a longtime conservative fundraiser. "Conservatives are going to be methodical about it, working in the churches and doing groups on the ground."
Activists are racing to turn emotions into contributions for grass-roots organizing and ads and, in November, votes.
"President Obama has made this an issue in the campaign and we are confident that Mitt Romney will eagerly defend the voters of these states against the president's attempt to impose same-sex marriage on the nation," said Brian S. Brown, president of the National Organization for Marriage.
Groups focused on a broader portfolio of issues say gay marriage will be one of several social issues on their agendas but that none will be emphasized as prominently as Obama's performance on the economy.
Before Obama's announcement, Reed's Faith & Freedom Coalition was preparing a voter guide and social media campaign that included gay marriage with other social issues.
"The only thing that's changed now is that we can say that Obama himself has come out and stated that he's for single-sex marriage," Reed said.
Roberta Combs, president of the Christian Coalition of America, a conservative grass-roots group, didn't need Boehner's counsel to know that Obama's support for gay marriage shouldn't play a leading role in the election. She's seen the polls that show America roughly split over gay marriage, although with support for it growing, as well as surveys that leave no doubt voters remain jittery about the economy and their personal finances.
"I don't want to see the election just based around social issues," Combs said. "You can't keep Americans' minds off of the economy."