Democrats are down to the final four senators remaining who have not expressed a pro-gay-marriage stance.
Arkansas Sen. Mark Pryor, West Virginia Sen. Joe Manchin, Louisiana Sen. Mary Landrieu, and South Dakota Sen. Tim Johnson have not backed gay marriage. Next year, Pryor and Landrieu face re-election in their red states and Johnson will retire.
North Dakota Sen. Heidi Heitkamp and Indiana Sen. Joe Donnelly announced on Friday their support for gay marriage, citing the changing makeup of families. Neither senator is up for re-election until 2018.
“I have concluded the federal government should no longer discriminate against people who want to make lifelong, loving commitments to each other or interfere in personal, private, and intimate relationships,” Heitkamp said in a statement.
In a Facebook post, Donnelly said he voted to repeal the “Don’t Ask, Don’t Tell” policy, and opposes amending Indiana’s or the country’s constitutions to “enshrine in those documents an ‘us’ and a ‘them,’ instead of a ‘we.’”
Heitkamp and Donnelly, who both represent red states, are the most recent legislators to come out in support of gay marriage. Delaware Sen. Tom Carper and Florida Sen. Bill Nelson, both Democrats, backed gay marriage earlier this week.
From President Obama to former Vice President Dick Cheney, many prominent figures from both sides of the aisle have come forward to publicize their change of heart on marriage rights. Ohio Sen. Rob Portman and Illinois Sen. Mark Kirk are the only Republican senators who have reversed their previous anti-marriage-equality positions.
During the last week in March, the Supreme Court heard arguments for and against Proposition 8, a California law that bans same-sex marriages, and the Defense of Marriage Act (DOMA), a federal law that defines marriage as between a man and a woman. The judges might not make a decision about the constitutionality of the two laws until June.