President Obama has made it clear DOMA should be repealed. The Respect for Marriage Act, introduced in Congress in 2009, seeks to repeal the law.
His administration's "willingness to defend the letter of the DOMA law, and not the spirit of it, is an open door for those who want to redefine one-man, one-woman marriage by any means possible," said Horne.
Many states have constitutional bans on same-sex marriage, while others have passed laws through their legislatures.
"A majority of Americans support marriage, including voters in 31 states who have "defended the one-man, one-woman definition of marriage at the ballot box," she said.
But for the first time, more than half of all Americans (52 percent) said they would support the federal government giving "legal recognition to marriages between couples of the same sex," according to a recent poll from the AP-National Constitution Center.
Only 46 percent supported such marriages in 2008.
"We are at a historically significant moment," said lawyer Soloway.
The Constitutional problem with DOMA is that states have historically controlled family law in issues of marriage, parenting and inheritance, according to Jennifer Pizer, senior counsel at Lambda Legal and director of the National Marriage Project.
"Congress should not be interfering in the way that DOMA does," she said.
So far, two cases have challenged DOMA as a violation of the 10th amendment that honors the authority of states and prohibits intrusion by the federal government.
Ultimately, say advocates, the courts will intervene when they determine state laws against same-sex marriage violate the Constitution's respect for individual liberties and state rights.
"Congress missed its power," said Pizer.
"Same-sex couples are not like a generation ago, when they consigned themselves to unhappy heterosexual marriages because following their own dreams was not possible," she said. "Now there is a visibility of gay people in all walks of life who can follow their heart and lead a fulfilling and not a miserable life."
Such was the case with Vandiver and Velandia, who created a Facebook page -- Save Our Marriage -- that in just one week has more than 6,000 supporters.
"It's sad how many people are affected by DOMA," said Velandia. "But it's pretty nice we can help."
Vandiver is optimistic that "equality and fairness will win," but he said, "No one should lose a spouse when a law is in dispute for being unconstitutional."
"I never imagined it was possible that a spouse could be taken away by the government and deported to another country and forced to leave," said Vandiver. "They threaten to take away the thing you love the most."