Ohio seems to be the epicenter of a seismic shift in public opinion on same-sex marriage.

As the Supreme Court deliberates two high-profile cases — California’s Proposition 8 and the 1996 Defense of Marriage Act — many analysts are observing, “As Ohio goes, so goes the nation.”

In 2004 Ohioans voted to define marriage as a union between a man and a woman, effectively banning gay marriage. Just one of the state’s 88 counties – Athens – voted in opposition to a measure that passed with 62 percent of the vote.

A new poll showed a striking reversal in public opinion. A Saperstein poll, released March 24, showed that 54 percent of Ohioans now support a proposed new amendment, which would repeal the state’s 2004 ban on gay marriage and “allow two consenting adults to marry, regardless of their gender.”

Hamilton County, the home of Sen. Rob Portman, R-Ohio, voted in favor by 56-44 percent. Now Portman is on the other side, and his recent conversion, which evolved after his son Will came out to his parents in 2011, has raised a question once believed unthinkable in Ohio: Could a majority of the state’s voters actually support gay marriage?

Proponents and opponents alike believe that the answer could be “yes” — and that a potential ballot initiative, for which signatures are now being collected, actually has a chance of passing.

“It’s a dramatic change,” said John Feldmeier, professor of political science at Wright State University, who has researched the issue for decades. “We are taking big steps, not short steps.”

Just how big could be a question of debate. A Quinnipiac poll released in December showed that a slim majority of Ohioans — 47 percent — still oppose same-sex marriage, compared with 45 percent who support it.

Deborah Pryce, a former Ohio Republican Congresswoman, signed an amicus curiae brief submitted to the Supreme Court in the case of Hollingsworth v. Perry, which challenges California’s voter-approved ban on same-sex marriage known as Proposition 8. “The debate has reached a fever pitched because of the Supreme Court activity,” Pryce said. “I signed it because I feel strongly about it, and the brief was very well-written.”

Social conservatives, meanwhile, are saying, “Not so fast.” The Ohio Christian Alliance has been sharply critical of Portman’s March 14 announcement changing his position. “Our base is totally in favor of traditional marriage,” said OCA President Chris Long. “If they were to lose that, there wouldn’t be a Republican Party.”

Signatures are being collected for The Freedom to Marry and Religious Freedom Amendment, which would repeal the 2004 law and allow two “natural persons” to marry while exempting religious organizations from performing or recognizing marriages outside their beliefs. Ian James is co-founder of FreedomOhio, the group pushing to repeal Ohio’s same-sex marriage ban. James said that FreedomOhio is on track to collect the 385,245 signatures required for the Nov. 5 ballot by the July 3 deadline.

Feldmeier said FreedomOhio is taking a strategic risk by putting the issue on the ballot during an off-year election: “The voting demographics tend to be retired white voters, and that set isn’t likely to be predisposed to favor your issue. But it is the type of issue capable of igniting the college crowd, and it could drive young voters to the polls.”

James said the number of volunteers has more than doubled since March 14. ‘The Portman announcement brought incredible energy to the field,” James said. “It’s a father and mother showing great love for their son, and this incredible change of heart from father who supported the Defense of Marriage Act in 1996.”

Long takes umbrage with the expression “change of heart.”

“It’s a policy position change he has done,” he said. “The feedback we’re getting is that people feel betrayed.” In the OCA press release after Portman’s announcement, Long wrote Portman “crossed a line and violated the trust of the voters that supported him in 2010, who believed that he carried with him into office the same traditional values that they hold so dear.”

Long said Portman undoubtedly will face a primary challenge in 2016 if he doesn’t retreat from his support for same-sex marriage.”This is a watershed issue for our members, and they will not vote for a candidate who does not hold view on traditional marriage,” Long said.

Other observers believe the issue will have little impact on Portman’s future political career. “It was a non-issue even for this election cycle, after President Obama came out in favor of gay marriage, and Portman is light years away from re-election,” Feldmeier said. “I would be shocked if this issue affected him positively or negatively, other than showing he has the courage of his convictions.”

Republican strategist Mark Weaver also believes Portman will suffer few political consequences. “He is so well-situated, with such a strong basis of support,” he said. “It’s probably a wash. There’s a small group that will not support him and probably a growing number who agree with him.”

Portman has not backed away from his stance but appears, at times, to wish he could change the subject. At a GOP Lincoln Day dinner in Butler County, he received a standing ovation from the crowd when he was announced as the keynote speaker. Instead of talking about gay marriage, Portman urged the Republican party to “change directions.”

Portman is the first sitting Republican senator to come out in favor of gay marriage; on Tuesday, Sen. Mark Kirk of Illinois became the second. Kirk returned to the Senate in January a year after suffering a stroke. In a statement he wrote, “Our time on this earth is limited. I know that better than most.”

Portman told us Wednesday he didn’t talk to Kirk about his decision, adding that he has received a generally positive response to his announcement. “People have been very respectful and I’ve had a lot of good conversations about it,” he said. “The No. 1 issue among my colleagues and my constituents isn’t that, but it is this economy, it is the deficit.”

Randy Borntrager, political director of the liberal-leaning People for the American Way, said that Portman’s and Kirk’s actions constitute “the first visible crack in a Republican party that has allowed itself to be ruled and taken over by the right-wing fringe.” The fact that Portman made front-page news all over the country, Borntrager said, “shows how far behind the party is when it comes to joining mainstream America.”

Borntrager added, “I am glad that Portman has come down on the right side of history, but his son is the real hero.”

Weaver, however, said the significance of the issue has been overblown: “I think too much has been made of this as an avatar of political change. The polls say what they say, but when you ask people the issues most important to them, gay marriage is way down on the list. I spend a lot of time reading polls, and it is below taxes jobs, unemployment health care foreign policy and terrorism.”

Some proponents of same-sex marriage have even criticized Portman for changing his mind because of his son, arguing that politicians should do the right thing without having a gay family member.

“It is surprising,” Weaver said. “That’s looking a gift horse in the mouth. I support traditional marriage, but it’s rather offensive for supporters of same-sex marriage to take a newcomer to their cause and dress him down for not coming to their cause soon enough.”

James is also frustrated by that response. “I think the two words that you’re looking for are ‘thank you,’” he said. “Senator Portman has freed other Republicans to support the freedom to marry. He’s a change agent for gay marriage.”

James isn’t surprised that it took some time for Portman to change his mind. “When I came out to my mom and talked about marriage, she was not there either,” he said. “The Portmans are the poster parents for acceptance and love and embracing marriage equality. When you had only 38 percent in favor of gay marriage in 2004, and 62 percent against it, don’t we need a lot of people to have change of mind and heart?”