Sen. Bob Casey (D-Pa.) now supports gay marriage, he revealed in an interview with the Morning Call.
Having come to believe that the Defense of Marriage Act should be repealed, Casey decided that he could not take that stance without supporting gay marriage outright.
"I ultimately decided that to make a decision about DOMA was making a decision about marriage equality itself," the Catholic senator said.
Over several days Casey crafted a statement announcing his decision.
"If two people of the same sex fall in love and want to marry, why would our government stand in their way? At a time when many Americans lament a lack of commitment in our society between married men and women, why would we want less commitment and fewer strong marriages?" it reads in part.
A letter from a lesbian constituent detailing the higher taxes she and her partner paid compared to a married couple influenced his decision, Casey said: "As a Senator and as a citizen, I can no longer in good conscience take a position that denies her and her family the full measure of equality and respect."
There are now only eight Democratic senators who do not support gay marriage: Tom Carper (Del.), Joe Donnelly (Ind.), Heidi Heitkamp (N.D.), Tim Johnson (S.D.), Mary Landrieu (La.), Joe Manchin (W.V.), Bill Nelson (Fla.) and Mark Pryor (Ark.).