tim_johnson_ap_605 Rep. Tim Johnson (D-S.D.) (Associated Press)

Sen. Tim Johnson (D-S.D.) on Monday became the latest Democratic senator to embrace gay marriage.

"After lengthy consideration, my views have evolved sufficiently to support marriage equality legislation," Johnson said in a statement released through his office. "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."

Johnson's decision comes in the wake of several other Democratic senators who have switched in favor of gay marriage. Just three red-state holdouts remain: Sens. Mary Landrieu (D-La.), Joe Manchin (D-W.Va.) and Mark Pryor (D-Ark.).

Landrieu and Pryor are both up for reelection in 2014, as was Johnson before he decided not to seek another term.

Johnson's son, U.S. Attorney Brendan Johnson (D), is considered a top potential contender for his seat, as is former congresswoman Stephanie Herseth Sandlin (D). Former governor Mike Rounds is running on the GOP side.

Just two sitting GOP senators — Rob Portman (Ohio) and Mark Kirk (Ill.) — support gay marriage.

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