Voters in Maryland and Maine on Tuesday approved measures to allow same-sex marriage, the first time gay marriage has been approved by statewide popular votes.

In all, voters in four states – Maine, Maryland, Washington and Minnesota - considered ballot measures Tuesday on the issue of same-sex marriage.

Minnesota voters rejected a proposed constitutional amendment to define marriage as between a man and a woman by a margin of 51 percent to 49 percent, NBC News projected Wednesday morning. In Washington, the vote was still too close to call; however with just over half of the vote counted, the same-sex referendum was leading 52 to 48 percent, according to NBC’s electoral map.

Proponents of same-sex marriage celebrating their first popular vote victories.

“Tonight we’ve taken the talking point away that marriage equality cannot win at the ballot box,” said Fred Sainz, vice president of communications with the Human Rights Campaign, which invested millions of dollars in same-sex marriage initiatives.

Sainz gave some of the credit for the victory to President Barack Obama’s support for same-sex marriage.

The president said that his decision was informed by speaking with Americans including servicemen and women he met during the work to end Don’t Ask Don’t Tell.

Obama’s challenger, Mitt Romney, had said that he would support and champion legislation defining marriage as between a man and a woman.

Sainz said he thought Americans have become more understanding of why gay and lesbian couples want to marry.

“The hearts and minds of the American public have changed,” he said. “For years now we’ve been having a long extended conversation and connecting with them about how marriage equality is about love, family and commitment, which are common human factors."

Opponents of same-sex marriage dismissed that argument, however. Brian Brown, president of the National Organization for Marriage, noted that dozens of states have passed laws in recent years defining marriage as between a man and a woman.

He called states like Maryland “the most liberal of liberal states” and not a proxy for the general population.

“For the gay marriage groups to win in the most liberal states is not a tipping point at all,” Brown said.

The measures came as Americans appear to be growing more comfortable with the idea of gay marriage.

A Pew Research Center poll this summer found that 48 percent of Americans favor same-sex marriage, up from 31 percent in 2004.

Democrats were the strongest proponents, with 65 percent favoring same-sex marriage in the Pew survey. Only 24 percent of Republicans favor gay marriage, while 51 percent of independents favor it.

Although these are the first statewide voting victories for gay marriage, gay marriage has been legalized in some states through legislative or court action. Those include Massachusetts, Connecticut, Iowa, Vermont, New Hampshire, New York and the District of Columbia, according to the National Conference of State Legislatures.

More than 30 states, including Arizona, Colorado and Texas, have laws or constitutional provisions defining marriage as between a man and a woman, according to the National Council of State Legislatures.

Here’s a look at the four states that voted on the issue in this election.

Maine: This was the second time voters in Maine were faced with a decision over same-sex marriage. A bill allowing same-sex marriage was passed by the state legislature in 2006, but voters overturned it in 2009.

Maryland: In Maryland, voters were asked to uphold a law allowing same-sex marriage that the governor signed into law last March.

Minnesota: In Minnesota, voters were asked whether the state constitution should explicitly define marriage as between one man and one woman. Gay marriage is already banned under state law; writing the ban into to the constitution, proponents argued, would have protected the amendment from being overturned in the future.

Washington: In Washington state, the legislature approved same-sex marriage earlier this year, and the law was scheduled to take effect in June. But opponents of the law were able to get a referendum on the ballot asking voters if they want to uphold the law.

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