But in an interview this afternoon with ABC's Robin Roberts, Obama's evolution is apparently complete.
"I have to tell you that over the course of several years as I have talked to friends and family and neighbors when I think about members of my own staff who are in incredibly committed monogamous relationships, same-sex relationships, who are raising kids together, when I think about those soldiers or airmen or marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that Don't Ask Don't Tell is gone, because they are not able to commit themselves in a marriage, at a certain point I’ve just concluded that for me personally it is important for me to go ahead and affirm that I think same sex couples should be able to get married.”
A Gallup Poll released Tuesday showed that half of Americans support legalizing gay marriage, up from 44 percent in 2010.
Obama's announcement comes on the heels of statements of support by Vice President Joe Biden, who said on Sunday's "Meet the Press" he's "absolutely comfortable" with same-sex marriage, and by Secretary of Education Arne Duncan.
The presumptive GOP nominee, Mitt Romney, said Tuesday that he "does not favor marriage between people of the same gender, and [he does] not favor civil unions if they are identical to marriage other than by name."