March 18, 2013 -- For Mark Uhron, it was his clients' financial entanglements that led to a change of heart on gay marriage.
"I'm dealing with a lot of clients now who have partners and don't know if benefits are going to get extended to them. It complicates their whole financial picture," Uhron, a white, Catholic, conservative Republican and financial adviser in Vienna, Va., told ABC News.
"I just think that it should be a state decision," said Uhron, a Navy veteran who knew of service members discharged for being gay before the military instated its since-repealed "don't ask, don't tell" policy. "I suppose same-sex couples have every right to be as miserable as the rest of us, so why shouldn't they be allowed to get married?"
Infographic: Growing Support for Gay Marriage
Uhron, 58, is part of a recent boom of Americans who think gay marriage should be legal.
The most recent ABC News-Washington Post survey, released today, finds a substantial swing in support of same-sex marriages in the past decade. A record-high 58 percent of Americans think gay marriage should be legal, according to the new ABC-Post numbers, an increase of 26 percentage points since the 32 percent recorded in 2004. Thirty-six percent now say gay marriage should be illegal.
Read more: Rob Portman supports gay marriage
The poll follows two major public endorsements for gay marriage.
Ohio Republican Sen. Rob Portman last week became only the second sitting GOP senator to ever endorse gay marriage, announcing his shift in an op-ed and TV interview. Former secretary of State Hillary Clinton offered her public support today.
See More: Same-Sex Marriage Status in the U.S. By State
The trend cuts widely across demographics. Liberals and 18-29 year olds were the most supportive of gay marriage, at 58 percent and 57 percent, respectively. The biggest upticks came among nonwhites, whose support for gay marriage grew by 33 percentage points since 2004, to 61 percent from 28 percent. The second-biggest swing came among moderates, whose support jumped by 31 points, to 71 percent in 2013 from 40 percent in 2004.
Watch: Obama Affirms Support for Same-Sex Marriage
But even some unexpected groups have seen gay-marriage support rise by stunning rates since 2004, and nearly every demographic group has upped its backing for gay marriage by at least 23 percentage points since then.
Among white evangelical Protestants, 7 percent of whom backed gay marriage in 2004, support grew by 24 percentage points to 31 percent in 2013. Among conservatives, support grew to 33 percent from 10 percent. Among Americans 65 and older, support grew to 44 percent from 18 percent.
Support grew the least among Republicans (to 34 percent in 2013 from 16 percent in 2004) and Catholics (to 59 percent in 2013 from 40 percent in 2004).
Some supporters of gay marriage have held their views for a long time but have seen more vocal support in recent years.
"I've had gay friends since high school," said Chris Granneman, a moderate, independent, religious agnostic who voted for Barack Obama in 2008 and 2012, but who isn't happy with the president.
Granneman told ABC News he doesn't know whether homosexuality is a choice, and he thinks states should be able to choose whether gay marriage is legal.
A 37-year-old maintenance worker and former salesman living in Oakville, Ind., Granneman said he doesn't think opinions on gay marriage have changed in his community, but he does think the discussion has.
"I think opinion has been pretty steady, but people are more comfortable voicing their opinions," Granneman said. "This is the Bible-belt Midwest. There's a bunch of pretty hardcore religious conservatives around here, and I think that people probably didn't express their opinions before.
"I think the majority of people are all about people being able to do what they want. Land of the free, home of the brave, right?"
Unlike Granneman, most Americans now think being gay is just something people are born with: 62 percent now see it that way, up from 49 percent in 2004. Meanwhile, 24 percent now see being gay as a choice.
Read more: Hillary Clinton Endorses Gay Marriage
Cole Trosclair, 32, a Jewish, liberal Democrat in Jefferson, La., said she has long thought that gay marriage should be legal under federal law and that gays are born with their sexual preference.
"I've felt this way for a long time," said Trosclair, a customs broker and freight forwarder. "I think a lot of it is just knowing people who are homosexual, you know. Just the belief that everyone should have equal rights. Growing up in the deep South and being Jewish, I've definitely seen both religious and racial persecution and bigotry, and I think homosexuality falls in the same category as somebody being different instead of somebody being wrong."
While gay marriage becomes more popular, some of its opponents remain firm in their belief that marriage is for a man and a woman only. Until very recently, that has been the norm among politicians as well: President Obama maintained that view through the 2008 election and only completed his public shift in opinion in May, endorsing gay marriage while saying policy should be left to the states, in his landmark interview with ABC News' Robin Roberts.
For some, opposition to gay marriage is driven by religious beliefs.
"We believe that because of the Bible and the standards that the Bible has put forth," said Amanda Keyes, 28, an evangelical Protestant living in Grayson, Ky. "We are pretty firm on that. We won't be changing the way we feel about that."
Keyes said homosexuality and gay marriage come up in discussion in her family's church community, and that their friends and acquaintances are unanimously opposed to legalizing same-sex marriage.
Keyes said she doesn't know many gay people, but that her husband has gay relatives. When they see each other at family gatherings, marriage policy isn't an issue.
"They kind of understand that that's how we believe, and they don't try to be pushy about it," Keyes said. "And, likewise, we don't try to hound them about it when we see them. ... It's kind of left at that."