"President Obama, who was against same-sex 'marriage' before he was for it, and his administration, which said the Defense of Marriage Act was constitutional before they said it was unconstitutional, has now flip-flopped again on the issue of same-sex 'marriage,' putting allegiance to extreme liberal social policies ahead of constitutional principle," Family Research Council President Tony Perkins said in a statement.

But there are signs of movement even among some high profile Republican leaders

The Republican-penned friend of the court brief, which is designed to influence conservative justices on the high court, includes a number of top officials from the George W. Bush administration, Mitt Romney's former campaign manager and former GOP presidential candidate Jon Huntsman.

It is also at odds with the Republican Party's platform, which opposes same-sex marriage and defines marriage as a union between a man and a woman.

Still, with White House and high-profile Republican support, legal and legislative victories in a number of states and polls that show an increasing number of Americans support same sex-marriage, proponents feel that the winds of history are with them.

"What we've seen is accelerating and irrefutable momentum as Americans have come to understand who gay people are and why marriage matters," Wolfson said. "We now have a solid national majority and growing support across every demographic. We have leaders across the spectrum, including Republicans, all saying it's time to end marriage discrimination."