WASHINGTON -- Supporters of same-sex marriage reached a major milestone in Tuesday’s elections, when Maryland and Maine became the first states where voters upheld marriage rights for gay and lesbian couples.

While gay marriage has gained the support of courts, state legislatures and even President Barack Obama, voters have rejected the question every time it has appeared as a ballot issue.

But Tuesday turned the tide. Washington state voters were poised to uphold gay marriage on Wednesday, with supporters of the referendum declaring victory. Voters in Minnesota turned down an effort to ban gay marriage in the state’s constitution.

“We can’t underestimate the importance of what we saw yesterday,” said David Masci, a senior researcher at the Pew Forum on Religion and Public Life. “It’s a pretty big deal.”

Part of it boils down to demographic changes, he said. Younger voters overwhelmingly backed Obama’s election in 2008 and turned out in even larger numbers on Tuesday. They’re also the group that shows the highest support for gay marriage.

Evan Wolfson, president of Freedom to Marry, a New York-based gay rights group, called the Election Day results “a powerful demonstration that the center of gravity has dramatically shifted in our direction” after losses at the ballot in 2004 and 2008.

“We’re working within a huge amount of wind in our sails,” he said.

Brian Brown, president of the National Organization for Marriage, which opposes same-sex marriage, downplayed the significance of the votes, saying they were the result of heavy political and financial support in four liberal-leaning states. All four – Maryland, Maine, Minnesota and Washington –voted to re-elect the president.

“Though we are disappointed over these losses, we remain faithful to our mission and committed to the cause of preserving marriage as God designed it,” Brown said in a statement. “Marriage is a true and just cause, and we will never abandon the field of battle just because we experienced a setback."

But the result in each of the four states, where gay marriage supporters prevailed by a roughly 52 percent to 48 percent margin, may reflect how Americans are evolving on the issue.

A Pew Research Center poll in July showed a nearly even split, with 48 percent of Americans supporting gay marriage and 44 percent opposing it. By comparison, in 2004, 60 percent were opposed to it and 31 percent were for it.

“Our nation is still divided on this issue, but the trends are heading in the direction only supporters can be happy about,” Masci said.

Broken down demographically, the contrasts grow even starker. Millennials – mostly Americans under 30 – backed gay marriage overwhelmingly, at 63 percent, according to the Pew poll. For people over 65, however, support falls to 33 percent. And both groups had been even lower in their support in 2004: 51 percent of millennials and 17 percent of the 65 and older age group.

In 2004, the year that Massachusetts became the first state to legalize same-sex marriage, voters in 11 other states banned it. Voters in California banned same-sex marriage in 2008 with Proposition 8.

But there has been a shift, with legislatures in New York, New Jersey, Maine, Maryland and Washington all passing gay marriage bills. With Tuesday’s results, gay and lesbian couples could soon marry in nine states and the District of Columbia. The U.S. Supreme Court could decide on Prop 8 or another gay marriage case this term, legal observers say.

Wolfson also attributes the change to the increased visibility of gay and lesbian couples and their families.

“2004 came before people had a chance to hear real gay families,” he said. “In the eight years since, there have been a lot of stories and conversations and a lot of progress that has resulted in wins.”