Sen. Tim Johnson (D-S.D.) announced his support for same-sex marriage on Monday, leaving just three Senate Democrats opposed to gay marriage.
“After lengthy consideration, my views have evolved sufficiently to support marriage-equality legislation,” Johnson said in a statement. “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.”
Over the last several weeks, a dozen Democrats and two Republicans have endorsed gay marriage, which polls suggest is now favored by a majority of voters.
Gay-rights advocates are hopeful that the growing public support will herald the striking down of prohibitions on same-sex marriage throughout the country.
The Supreme Court last month held hearings on cases challenging the constitutionality of California’s Proposition 8, which banned gay marriage in the state, and the federal Defense of Marriage Act (DOMA), which denies some benefits to same-sex partners.
Johnson follows Sens. Joe Donnelly (D-Ind.) and Heidi Heitkamp (D-N.D.), who announced their support for gay marriage on Friday. Sens. Mark Kirk (Ill.) and Rob Portman (Ohio) are the only Republicans to publicly back same-sex marriage.
In March, Johnson announced that he would not run for reelection.