In April 2013, support for the right of same-sex couples to marry reached a crucial milestone. With the endorsements of Democratic Sens. Bill Nelson, Heidi Heitkamp, and Joe Donnelly, a majority of U.S. senators supported marriage equality for the first time in history. The Senate now includes 56 supporters of marriage equality (or 57, if you count Louisiana Sen. Mary Landrieu, who says she personally supports it but also supports her state’s same-sex marriage ban.) After Tuesday’s elections, however, marriage equality is virtually certain not to enjoy majority support in the chamber.

Two incumbent Democrats who support marriage equality – North Carolina’s Kay Hagan, Colorado’s Mark Udall – lost their re-election bids to GOP challengers who oppose same-sex marriage.

Advertisement:

With 100 percent of precincts reporting in Alaska, Democratic Sen. and marriage equality supporter Mark Begich trails Republican challenger Dan Sullivan by 4 points, though it may be more than a week before the race is called because 38,000 early and absentee ballots remain to be counted.

Moreover, in West Virginia, South Dakota, Iowa, and Montana, pro-marriage equality Democrats retired and saw their seats picked up by anti-marriage equality GOPers.

Landrieu, meanwhile, faces a December 6 runoff against Republican marriage equality opponent Bill Cassidy, who leads Landrieu in head-to-head polls.

Advertisement:

So when the 114th Congress convenes in January, there will be only 49 or, if Begich pulls off a stunning come-from-behind victory, 50 supporters of marriage equality in the Senate. There may yet be a 51 vote majority -- if you count Landrieu and (an even bigger if) she manages to survive next month’s runoff.

If Landrieu loses, that will leave West Virginia Sen. Joe Manchin as the only Senate Democrat who opposes gay marriage. Democratic Sen. Mark Pryor of Arkansas, who also opposes marriage equality, lost his re-election bid to Republican Tom Cotton by double digits last night. Only four Senate Republicans – Susan Collins of Maine, Mark Kirk of Illinois, Lisa Murkowski of Alaska, and Rob Portman of Ohio – support same-sex marriage, while no GOP Senate candidate elected last night favors it.