This comes as President Barack Obama has changed positions on same-sex marriage over his political career. Now fully supportive, he's said would strike down California's law if he sat on the Supreme Court.
Other prominent politicians have voiced timely opinions in recent weeks, indicating the matter's importance in 21st century American politics.
Hillary Clinton, the former secretary of state and possible 2016 Democratic presidential candidate, publicly backed same-sex marriage earlier this month.
The Republican party has historically backed efforts to define marriage as only between a man and a woman. But there's been notable movement of late among Republicans, including Sen. Rob Portman's recent shift to support same-sex marriage, which he made two years after his son revealed to him that he is gay.
"There is no putting this genie back in the bottle. It is undeniable. The shift is here, and we're not going back," Republican strategist and CNN contributor Ana Navarro said Sunday.