Another Senate Democrat switched his position and came out in support of same-sex marriage today, leaving only three Democratic senators who have not endorsed marriage equality.

Sen. Tim Johnson, D -S.D., said in a statement sent today from his office that his views have "evolved" on the issue.

"After lengthy consideration, my views have evolved sufficiently to support marriage equality legislation," Johnson, 66, said.

"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."

This marks the 12th Senate Democrat in three weeks to reverse course and embrace same-sex marriage. The three Senate Democrats who continue to oppose marriage equality in some way: Sens. Joe Manchin of West Virginia, Mary Landrieu of Louisiana and Mark Pryor of Arkansas.

Two Republican senators have endorsed same-sex marriage: Sens. Rob Portman of Ohio and Mark Kirk of Illinois.