In his intentionally wrinkled button- down shirt, with trimmed hair and eager poise, Sam Adkisson is the kind of young Republican his party needs.
Adkisson, 20, a rising junior at Vanderbilt University in Nashville, Tenn., says he believes in the Republican creed of limited government and lower taxes. At the same time, he says, his party is wrong to oppose same-sex marriage.
He is part of the shift toward near-majority support for the right of gays to marry in the United States, a change propelled by adults ages 18 to 29 — a group that outnumbers the baby boom generation — according to polling at Harvard University's Institute of Politics. The move will have political consequences, especially for a Republican Party that already has lost ground among Hispanics and women as the gay-marriage issue tests the loyalties of younger voters.
Yet even as 12 states have approved some form of gay marriage, 30 states prohibit it, including 25 by constitutional amendment. Unless the Supreme Court offers a sweeping ruling later this month on the issue, Republicans will be trying state-by-state to persuade young voters to back them and reject their peers.
"For my generation, the ship has sailed," Adkisson said in an interview. "With my generation especially, equality under the law, we are going to support it almost everywhere."
Unlike comparatively consistent views about guns and abortion among students, Adkisson said, "gay marriage is the one issue where I do see a shift, and a tangible one."
Even in Tennessee, which banned gay marriage by constitutional amendment in 2006 with the support of 81 percent of voters, there are signs of change. Vanderbilt University released a poll May 12 showing 49 percent of those surveyed favored either same-sex marriage or civil unions. Among those under 30, support ran at 69 percent.
"The whole country is moving toward gay rights broadly," said John Geer, chairman of political science at Vanderbilt, who oversees the poll. "Tennessee is part of that, not in the same place as Massachusetts but moving in the same direction."
And young adults are driving the change. John Della Volpe, director of polling at Harvard's Institute of Politics, said surveys of millenials — people born between 1980 and 2000 — showed they either favored recognizing same-sex marriage or said they didn't care by a ratio of 3-to-1.
"This is saying that 26 percent of young Americans don't believe it should be recognized," Della Volpe said. "This demographic group that we are polling is the largest generation in the history of America, larger than baby boomers; most are of age, and they will continue to become a more important force in elections."
The Institute of Politics survey also showed little regional variation in support, though opposition to gay marriage was highest in the South, at 31 percent.
Michael Feldman, a Democrat who graduated from Vanderbilt in May, saw his fellow students' views change during their four years on campus, often because he had friends who were gay or because of exposure to entertainment that embraced gay marriage.
"I really do think it has a lot to do with the fact that all my friends watch ''Modern Family,' '' said Feldman, referring to the ABC television show that features a gay married couple. ''Shows like that have an effect to neutralize a stigma if there was one.''
Indeed, Democratic political leaders only recently came to support gay marriage as well. Vice President Joe Biden announced in June 2012 that he supported the rights of same-sex couples. Six months later, President Obama endorsed it, and he was followed by former President Bill Clinton and former first lady and Secretary of State Hillary Clinton.
Numerous Democratic senators joined in, as did Sen. Rob Portman, R-Ohio, whose son is gay, and Sen. Mark Kirk, R-Ill., this year.
It is a swift march from the 2008 presidential campaign when former Arkansas Gov. Mike Huckabee expressed his views by saying marriage should be between ''Adam and Eve, not Adam and Steve,'' to laughter in the audience.
Still, there are structural impediments to how far the movement will go, and how quickly. State constitutional amendments often require two-thirds votes in legislatures to overturn, an unlikely prospect.
The most recent effort to approve same-sex marriage, in Illinois, failed on May 31 as supporters in the Democratically- controlled legislature pulled the bill before a vote they said would not pass even with the backing of Obama, Gov. Pat Quinn and Chicago Mayor Rahm Emanuel.
''It is a struggle to explain to my gay friends that although I love them and support them and will always be there for them, that doesn't mean I support all of their behavior,'' said Lisa Lacayo, who graduated from Vanderbilt in May and will be part of the Teach for America program in Texas.
Lacayo, who said her views are rooted in her Catholic religion, said states should decide the matter, and she would abide by a legislature's decision either way.
In Tennessee, the legislature is moving to solidify opposition to same-sex marriage. It designated Aug. 31 as ''ido4life Traditional Marriage Day,'' based on a resolution that read in part: ''Whereas, in Genesis 2:24, matrimony is delineated; it is expressed only between a man and a wife.''
Earlier in the session, state Sen. Stacey Campfield, R, offered legislation that opponents called the ''Don't Say Gay'' bill because of provisions they said would prohibit teachers from talking about anything other than heterosexual relationships. The bill failed, though Campfield plans to bring it up again during the next session.
Campfield, in an email response to questions, said he questioned the premise that attitudes on the issue had shifted.
''When put on the actual ballot, homosexual marriage has seldom passed on its own and I think has only passed by ballot initiative in small-population, liberal states,'' he wrote. ''As for youth polling, young people often say and do things completely different when they actually grow up, get a real job, begin paying taxes and start trying to raise a family.
''If we left all decisions up to youth polling,'' he wrote, '''beer pong' would be an Olympic sport.''
Like much of the South, Tennessee is buffeted by cultural crosscurrents. The state Capitol, built before the first shots of the Civil War, rises above the city, its tower visible from several miles away. The Greek Revival Structure embodies the state's history and traditions. Portraits of presidents such as Andrew Jackson and governors of both parties line the walls.
At the Information Desk, an enlarged $20 bill issued by the Confederacy sits alongside a brochure about the building. Upstairs, a bronze bust of Nathan Bedford Forrest, a Confederate lieutenant general who also played a role in founding the Ku Klux Klan, holds a place of honor among other Tennesseans.
Tennessee's stance on gay marriage has had little impact on its economy. The state has outpaced most since the recession ended in 2009, with the fourth-fastest growth in employment in the three-year period from December 2009 to December 2012, according to Bloomberg Economic Evaluation of States data.
The Capitol sits above Nashville's gleaming downtown, its job market robust relative to much of the nation thanks to health-care companies including HCA Holdings, Inc., and the country music industry, with 200 recording studios. It is home to Thomas Nelson, one of the world's largest Bible publishers.
''The Nashville metropolitan statistical area is already riding a wave of employment expansion," a report from the Federal Reserve Bank of Atlanta said.
A new convention center, "The Music City Center," opened in May.
"Tennessee is a conservative state, but not as conservative as the late-night TV shows would have you believe," Geer said. Still, he said, Republicans should be concerned about how they are connecting with younger adults.
In 2012, Obama benefited in re-election from the overwhelming support of Hispanics and younger voters as well.
"Looking at the 2012 data, you look at the Latino vote, and I would be more worried about the youth vote," Geer said. "The youth, a lot of them, want to be Republican because of small government, trust in free markets, and then they see this intolerance and they don't like it."
"There is an underlying component to America about equality," Geer said. "Sometimes we get to positions of equality and in an ugly fashion, but we get there."