Unlike in 2004, the Republicans face an economic downturn, an unpopular president, and Democrats making gains among voters in party affiliation, says Dr. Cain.
Nationally, 27 percent of Republicans now rank gay marriage as a major issue, according to research by the Pew Center. Since 2005, public opinion on the issue has stabilized, with 55 percent opposed and 36 percent in favor.
"Now the question is whether this brings it back as an issue. The historical pattern suggests there might be some greater visibility, but this has not been a major issue for a few years, so we'll have to wait and see what happens," says Carroll Doherty, associate director at the Pew Research Center for the People & the Press.
An upgrading of the issue might spell trouble for Democrats.
Voters in Florida – a potential battleground state – will vote on a ballot initiative in November to ban same-sex marriage that could galvanize conservatives to vote.
There's also a question mark around the reaction of evangelical voters, who have recently begun to drift away from the GOP. There are reasons to suspect this ruling won't affect that shift greatly, says Ivan Strenski, a professor of religious studies at the University of California at Riverside. "We know that that shift among Evangelicals is partly a generational one, and we know that in the younger generations, they don't care about this."