And then there were three...

Haraz N. Ghanbari / AP Sen. Tim Johnson, D-S.D.

Sen. Tim Johnson (S.D.) leaves the Final Four. There are now only three Senate Democrats who oppose gay marriage—Joe Manchin (W.Va.), Mark Pryor (Ark.), and Mary Landrieu (La.).

“After lengthy consideration, my views have evolved sufficiently to support marriage equality legislation,” said Johnson. “This position doesn’t require any religious denomination to alter any of its tenets; it simply forbids government from discrimination regarding who can marry whom.”

Two weeks ago, Johnson announced that he was not going to seek a fourth term, and retire in 2014. In the weeks since, many of Johnson’s colleagues have flipped on the gay marriage issue, including: Heidi Heitkamp (N.D.), Joe Donnelly (Ind.), Bob Casey (Pa.), Kay Hagan (N.C.), Jon Tester (Mont.), and Mark Warner (Va.). Claire McCaskill (Mo.) switched her stance a day before Johnson’s retirement announcement.

Johnson’s retirement gives him some room to maneuver in his socially conservative state. In 2006, South Dakota banned same-sex civil unions and domestic partnerships with a constitutional amendment backed by 52% of voters. South Dakota defined marriage as a union between a man and a woman back in 1939.

There are now 54 sitting Senators who endorse same-sex marriage.