South Dakota Senator Tim Johnson on Tuesday said the road to his Monday endorsement of gay marriage had been “slow.”

Johnson on Monday became the latest senator to publicly announce his support for marriage equality, leaving only 3 Democratic senators opposed.

Johnson said in a statement that his “views have evolved sufficiently to support marriage equality legislation.”

“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.”

In remarks to the Argus Leader on Tuesday, Johnson said that he reached his new stance after a “long process of thinking it through.”

“It was a long process of thinking it through,” Johnson said. “Like the president and the other [53] senators, I came to the conclusion slowly and carefully.”

“Each religious entity can maintain their support or opposition to same-sex marriage. It made no sense to me that marriage necessarily should have a religious quality to it.”

Johnson predicted that supporting marriage equality would “not at all” hurt a candidate in South Dakota. He added that response had been “mostly positive.”

Last month, Johnson, 66, announced that he would retire in 2014.

Only three Democratic senators remain opposed to marriage equality. Arkansas Senator Mark Pryor recently said he's “in the undecided category,” while Louisiana Senator Mary Landrieu said she has to honor her state's “very strong constitutional amendment against gay marriage.” The third holdout is West Virginia Senator Joe Manchin.