Sen. Tim JohnsonTimothy (Tim) Peter JohnsonCourt ruling could be game changer for Dems in Nevada Bank lobbyists counting down to Shelby’s exit Former GOP senator endorses Clinton after Orlando shooting MORE (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.” 

Sens. Joe ManchinJoseph (Joe) ManchinPavlich: The claim Trump let the mentally ill get guns is a lie Toomey to introduce bill broadening background checks for firearms Scott Walker backs West Virginia attorney general in GOP Senate primary MORE (W.Va.), Mary LandrieuMary Loretta LandrieuProject Veritas at risk of losing fundraising license in New York, AG warns You want to recall John McCain? Good luck, it will be impossible CNN producer on new O'Keefe video: Voters are 'stupid,' Trump is 'crazy' MORE (La.) and Mark PryorMark Lunsford PryorMedicaid rollback looms for GOP senators in 2020 Cotton pitches anti-Democrat message to SC delegation Ex-Sen. Kay Hagan joins lobby firm MORE (Ark.) are the only Democrats in the Senate who remain opposed to gay marriage. 

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 DonnellyJoseph (Joe) Simon DonnellyDemocrats now attack internet rules they once embraced Dem group launches M ad buy to boost vulnerable senators Senate rejects Trump immigration plan MORE (D-Ind.) and Heidi HeitkampMary (Heidi) Kathryn HeitkampSenate rejects Trump immigration plan Cramer to announce North Dakota Senate run on Friday Senate Democrats not sold on bipartisan immigration deal MORE (D-N.D.), who announced their support for gay marriage on Friday. Sens. Mark KirkMark Steven KirkHigh stakes as Trump heads to Hill Five things to watch for at Trump-Senate GOP meeting Giffords, Scalise highlight party differences on guns MORE (Ill.) and Rob PortmanRobert (Rob) Jones PortmanCommittee chairman aims for House vote on opioid bills by Memorial Day Flake to try to force vote on DACA stopgap plan Congress punts fight over Dreamers to March MORE (Ohio) are the only Republicans to publicly back same-sex marriage.

In March, Johnson announced that he would not run for reelection.