That is the analysis of a new study of the data by two pollsters, one a Democrat and the other a Republican.
"Significant opposition to the freedom to marry is increasingly isolated within narrow demographic groups while a much broader and more diverse majority are ready to let same-sex couples marry," wrote Joel Benenson, who led President Barack Obama's polling operation in 2008 and 2012, and Jan van Lohuizen, who did the same job for former president George W. Bush.
Their research, which will be released today, was commissioned by Freedom to Marry, an organization that promotes establishing a national right to same-sex marriage. It is a follow-up to a May 2011 report in which the pollsters found that support for such unions was accelerating, starting around 2009.
That appeared to be borne out by the 2012 election results. Until last year, voters had rejected same-sex marriage every time it had been put to the test in statewide elections. But in 2012, all four states with ballot questions on the issue either voted in favor of allowing such unions or rejected a ban on them.
Benenson noted that the question was not asked on exit polls in 2004 and 2008. Overall, the 2012 exit polls, which were conducted in 31 states, showed 49 percent supporting same-sex marriage in their states and 46 percent opposing it.
The pollsters found that opposition centered primarily in a few demographic groups.
Voters age 65 and older expressed opposition to allowing such unions in their states, by a 21-point margin, with 37 percent supporting them and 58 percent opposing. Those younger than 65 favored them by eight points, 52 percent to 44 percent.
The disparity was even greater among religious groups, broken down along racial lines. White evangelical Christians opposed same-sex marriage by nearly 3 to 1. But every non-evangelical group - white Protestants, white Catholics, Hispanic Catholics, African American non-evangelicals and Jewish voters -- expressed support for such unions by double-digit margins.
Meanwhile, African American voters who described themselves as evangelical or born again were narrowly divided, with 47 percent saying it should not recognize same-sex marriage and 45 percent saying it should.
Another "pocket of opposition," the pollsters said, is white voters who do not have a college degree. Only 40 percent of them supported same-sex marriage, compared with 56 percent who oppose it. Other groups supported such unions by 54 percent to 38 percent among non-white, non-college graduates; 56 percent to 41 percent among white college graduates, and 58 percent to 35 percent among non-white college graduates.
The report comes as the Supreme Court is about to consider two major cases involving same-sex marriage - one addressing the Defense of Marriage Act, which restricts the federal government from recognizing such unions performed in those states where they are legal, and the other on the constitutionality of California's ban on same-sex marriage.
In an interview, Benenson said the study suggests that lawmakers and candidates who embrace such unions are not likely to be punished politically, because "the American people are already there."
"Demographics is a big part of it," Van Lohuizen added, "but I also think there is a lot of rethinking going on."
However, David Lane, who organizes conservative Christians nationwide, said that the more than 65 million Americans who identify themselves as evangelicals are already feeling increasingly alienated from electoral politics.
If GOP leaders embrace same-sex marriage, he predicted, "it will lead quickly to the collapse of the Republican Party," causing a core constituency to leave for a third party or to renounce politics.
"The debate is good," Lane added. "We need to decide whether we are a Christian nation or a pagan nation and get on with it. The glory of a nation lies in its righteousness."
As he did for the past several election cycles, Lane is trying to mobilize evangelicals by organizing pastors and voters through the American Renewal Project, an organization that helped galvanize support for California's Proposition 8, which is being reviewed by the U.S. Supreme Court.
Ralph Reed, head of the Faith and Freedom Coalition, added that a Supreme Court decision in favor of same-sex marriage may anger the opposition.
"Look, if the Supreme Court does with marriage what it did on abortion, which is to impose the laws of New York and Massachusetts and impose them on the rest of the country by judicial fiat, it will make this issue more divisive and contentious, not less so," he said.
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