WASHINGTON — Three of them are retiring from Congress. One has a gay son. One followed the lead of his church, and others said they were concerned primarily with religious liberty protections.
When President Biden signed the Respect for Marriage Act on Tuesday in a splashy outdoor ceremony at the White House, he was surrounded by some of the 12 Republican senators whose support helped push it across the legislative finish line. The measure mandates federal recognition for same-sex and interracial marriages and overturns the Defense of Marriage Act.
The success of the legislation has reflected a tectonic shift in views in the United States on same-sex marriage, once a deeply divisive political issue but now something that about 70 percent of Americans — including a majority of Republicans — support, according to recent polls.
Still, the vast majority of House and Senate Republicans opposed the bill, and finding enough G.O.P. senators to pass it was not easy. In the end, supporters won over more than the 10 Republicans needed to break a filibuster. They were lobbied by their colleagues, by prominent gay donors and operatives in their party, and by religious groups who secured stronger religious liberty provisions.
Senator Roy Blunt of Missouri
One of only two Republicans in leadership to vote for the bill, Mr. Blunt is retiring from Congress in January, sparing him any political consequences for supporting it. While he is a conservative, Mr. Blunt has at times broken from his party to support bipartisan initiatives, such as a gun safety measure that became law this year, a bill last year to raise the debt limit and the $1 trillion infrastructure package.
Mr. Blunt said he would support the same-sex marriage legislation after it was amended to include religious liberty protections.
Senator Richard Burr of North Carolina
Mr. Burr also is retiring in January. Although he said little publicly about the legislation, his colleagues saw his vote as typical for him. In 2010, Mr. Burr voted to repeal the policy known as “don’t ask, don’t tell,” which barred openly gay and bisexual people from serving in the military, calling the policy “outdated.”
Senator Shelley Moore Capito of West Virginia
Ms. Capito is another Republican who, while conservative, has sometimes been willing to break with her party on major legislation, such as the gun safety compromise bill earlier this year and efforts to lift the debt ceiling. She was also a lead negotiator on the bipartisan infrastructure legislation. In announcing her support for the same-sex marriage bill, Ms. Capito said she was won over only after religious protections were added.
“This does not lessen the traditional sanctity of marriage or jeopardize the freedom of religious institutions,” she said in a statement.
Senator Susan Collins of Maine
One of the more moderate senators in her party, Ms. Collins was the lead Republican negotiator on the marriage bill, working closely with Senator Tammy Baldwin, Democrat of Wisconsin, to address concerns among her colleagues that the legislation would punish or restrict the religious freedom of institutions that refuse to recognize same-sex marriages.
Ms. Collins also worked closely with the outside group of G.O.P. donors and operatives, some of them gay, on a coordinated, $1.7 million campaign to persuade Republican senators that backing it would give them a political edge.
Senator Joni Ernst of Iowa
Ms. Ernst was the only member of Republican leadership in the Senate who is not retiring to support the measure. Ms. Ernst said that while her views on marriage have been evolving, the bill would “simply maintain the status quo in Iowa.”
Senator Cynthia Lummis of Wyoming
The first-term senator faced the most pressure to oppose the bill, especially after the other Republican senator from Wyoming, John Barrasso, voted against it. Ms. Lummis, who is a member of Trinity Lutheran Church, was pressed by the Wyoming Pastors Network to “reverse course” after she voted yes in a crucial test vote that paved the way for the bill to advance in the Senate. The Wyoming G.O.P. also admonished her for supporting the bill, which it claimed would threaten the state party platform.
But Ms. Lummis, her colleagues said, was determined.
“For the sake of our nation today and its survival, we do well by taking this step,” she said on the Senate floor last month, delivering an emotional speech about the need for more tolerance during what she called “turbulent times for our nation.”
Senator Lisa Murkowski of Alaska
Ms. Murkowski is a moderate who often veers from her party’s line, so her vote in favor of the legislation did not come as a surprise. In 2013, she was the third Republican senator to come out in favor of same-sex marriage.
Senator Rob Portman of Ohio
Another of the main negotiators on the bill, Mr. Portman first said publicly that he was in favor of same-sex marriage in 2013, after his son came out as gay. He had been a sponsor of the Defense of Marriage Act.
“It’s a change of heart from the position of a father,” Mr. Portman told Ohio reporters that year. His support for the same-sex marriage legislation reflects how the issue has garnered widespread bipartisan support across the country: Many people who once opposed same-sex marriage in the abstract have shifted their views on the issue because of relatives or close friends who are gay.
Mr. Portman is retiring from Congress.
Senator Mitt Romney of Utah
Mr. Romney has earned a reputation as something of a moderate, seeking bipartisan consensus when possible, although he remains conservative. A Mormon, Mr. Romney came out in favor of the legislation after the Church of Jesus Christ of Latter-day Saints, which historically has been opposed to gay rights, gave its support to the bill.
Senator Thom Tillis of North Carolina
Mr. Tillis was part of the bipartisan group of negotiators who worked to strike an agreement on the legislation that could draw additional Republican support. He was also one of the Republicans who worked with Democrats earlier this year on the bipartisan compromise that led to the enactment of the first gun safety legislation to pass Congress in years.
Senator Dan Sullivan of Alaska
Mr. Sullivan said he supported the bill because of the religious liberty provisions that were added during negotiations. In a statement, he said his vote was “much more about promoting and expanding religious liberty protections than same-sex marriage.”
Senator Todd Young of Indiana
In an op-ed in his hometown paper, Mr. Young said he had heard from many constituents disappointed in his decision to support the legislation. But, he said, “the explicit protections in this proposal offer far more in the way of religious liberty protections than currently under Obergefell,” referring to the 2015 Supreme Court decision that legalized same-sex marriage nationwide.
