It's been almost a year since President Obama announced his support for same-sex marriage, and the dominoes have steadily fallen as 54 of 100 U.S. senators - including two Republicans - have joined the cause's scaffolding. Retiring South Dakota Sen. Tim Johnson's announcement Monday that his "views have evolved sufficiently to support marriage equality legislation" whittles the number of outlying senators in the Democratic Caucus to three: a number that will likely stand until the 2014 midterm elections.
Johnson, who announced last month he would not seek reelection, said in a press release that "lengthy consideration" brought him around to backing same-sex marriage. "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," he said.
His revelation leaves three remaining Democrats who have not endorsed the position: Sens. Joe Manchin, D-W.Va., Mary Landrieu, D-La. and Mark Pryor, D-Ark. All have indicated their stances are relatively anchored.
"I believe that a marriage is a union between one man and one woman," Manchin, one of the most conservative Democrats in Congress, said in a statement to Bloomberg News. "My beliefs are guided by my faith, and I support the Defense of Marriage Act."
DOMA, which defines marriage as being between a man and a woman, is one of two laws being challenged against the Constitution before the Supreme Court; the other is California's gay marriage ban, Proposition 8.
Days after protestors on both sides of the issue flooded the court steps outside arguments for the cases, Sen. Mark Kirk, R-Ill. - one of Manchin's closest friends on the Hill - became the second Republican senator in a month to come out in favor of marriage equality. Earlier in March, Sen. Rob Portman, R-Ohio, turned a 180 from his historically staunch opposition to same-sex marriage after his son came out to him as gay.
Democrats Landrieu and Pryor, meanwhile, are both up for reelection next year in reliably Republican states - the likely basis for their refusal to join their party. Both have remarked on their positions.
"My views have evolved on this," Landrieu told CNN. "But my state has a very strong constitutional amendment against gay marriage and I think I have to honor that." According to Monroe, La., CBS affiliate KNOE, Landrieu clarified that her personal views differ from her political views: Her personal belief is that a person should be able to marry whomever he or she chooses.
Pryor, meanwhile, told Ft. Smith, Ark., CBS affiliate KFSM over the weekend that while he opposes same-sex marriage, he's "undecided" on whether to grant same-sex couples federal benefits.
"I am opposed to gay marriage," he said in an e-mail, but added on benefits: "This is one that is an evolving issue in Washington. I haven't really analyzed this in terms of benefits and what that does for the federal budget, (the) federal impact of this, and I'm sure as the gay marriage decision goes through the U.S. Supreme Court and all the ramifications for that over the next few months, we'll spend some time on this.
Speaking with reporters Monday, White House press secretary Jay Carney praised the national shift toward marriage equality as a "remarkable evolution," but said President Obama "was not and is not in a position to pass judgment" on the members of his party who have not backed same-sex marriage.