WASHINGTON — Senator Tammy Baldwin, the soft-spoken liberal Democrat of Wisconsin, was on a plane home from Washington last month when she got word that Senator Ron Johnson, her home-state colleague and a stridently hard-right Republican, had said publicly that he would not oppose a bill protecting same-sex marriage rights.
Seizing a rare moment in which she and Mr. Johnson — polar opposites by any measure — might agree on something, Ms. Baldwin tapped out a text to him saying she was thrilled.
“Don’t let them add anything obnoxious to it,” Mr. Johnson responded.
“I said I would do nothing to jeopardize its chances of passing,” Ms. Baldwin said in an interview in her Senate hideaway last week. “But we may differ on what constitutes ‘obnoxious.’ ”
Mr. Johnson replied with a thumbs-up emoji and wished her a pleasant weekend.
Ms. Baldwin, 60, who in 1999 became the first openly gay woman elected to Congress, has helmed the effort to win over the 10 Republican senators whose backing is necessary to secure passage of the Respect for Marriage Act, which would provide federal protections for same-sex marriage rights at a time of rising fears that they are at risk.
Now Ms. Baldwin, whose serene temperament and reserve have set her apart from her more press-preening and partisan colleagues, is in the spotlight as a pivotal player in a surprise legislative push, just weeks before midterm congressional elections, to ensure that rights for same-sex married couples will be recognized across the country.
So far, five Republicans, including Mr. Johnson, have stated publicly that they would support the legislation, which the House passed last month with an unexpectedly large fraction of G.O.P. votes. The others are Senators Susan Collins of Maine, Rob Portman of Ohio, Lisa Murkowski of Alaska and Thom Tillis of North Carolina.
Ms. Baldwin says that privately, at least five other Republicans have given her assurances that they would also support the bill when Senator Chuck Schumer, Democrat of New York and the majority leader, follows through on his pledge to bring it to the floor, likely sometime after Labor Day.
“More and more, my Republican colleagues know gay people who are married,” Ms. Baldwin said. “They see that the sky hasn’t fallen. Maybe some of them have gone to these ceremonies. Maybe some know that, but for that marriage certificate, their cousin wouldn’t have been able to see her wife in the hospital because she would have been a legal stranger.”
Democrats are pressing to enact the legislation in the wake of the Supreme Court ruling that overturned the nearly 50-year-old right to an abortion, amid concern that precedents legalizing same-sex marriage and protecting the rights of such couples could be the next to fall. In a concurring opinion in the abortion case, Dobbs v. Jackson Women’s Health Organization, Justice Clarence Thomas suggested that the court also “should reconsider” past rulings that established marriage equality and access to contraception.
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The House moved quickly to pass the same-sex marriage bill, as Democrats rushed to put themselves on the record on the issue and Republicans on the spot ahead of the elections. But 47 Republicans voted in favor — less than a quarter of the conference yet a larger proportion than expected — and Mr. Schumer said he would work to find the necessary votes to move it past a filibuster and to a vote.
In a matter of hours, a bill that many thought would be dead on arrival in the Senate became the subject of an intensive legislative push.
Ms. Baldwin, the epitome of Midwestern nice who enjoys sewing and cooking — hobbies she describes as “boring” — is in some ways an unlikely arm-twister for the effort.
Never one to seek attention, she played down the historic nature of her victory when she won her Senate seat 10 years ago, getting halfway through her speech before she mentioned that she was “well aware” that her election was a milestone for gay rights. (She also made history in 1999 with her election to the House, the first openly gay woman to serve there.)
Ms. Baldwin herself is not married, though she was in a domestic partnership that has since been dissolved.
The issue has defined her career in public office. Ms. Baldwin started working on marriage and domestic partnership legislation as a member of the Dane County board of supervisors and in the Wisconsin State Assembly in the 1990s, at time when, she said, “all the results were bad.”
The picture is far different today, she noted. Since 2015, when the Supreme Court established same-sex marriage rights, the number of Americans in such marriages has risen to more than 1.1 million. Elected officials in both political parties feel a more personal connection to the issue, and many see their families at imminent risk.
“People are literally frightened about whether their marriage will be dissolved by the court,” Ms. Baldwin said. “The important rights associated with marriage at the state level and federal level could evaporate.”
Still, the marriage equality bill has a narrow path in the evenly divided Senate, and Democrats are not taking any chances. Mr. Schumer, wary of banking on private commitments of support, has told Ms. Baldwin that he wants a buffer, and has her hunting for a few more Republicans to add to her “yes” column to comfortably account for any last-minute cold feet. (Still, Mr. Schumer has committed to bringing the bill up for a vote regardless of the final tally.)
Democrats and Republicans who support the measure were concerned, for instance, about whether Mr. Johnson, who said he saw “no reason to oppose” the legislation, could be counted as a reliable “yes” on any procedural vote to ensure passage. If he simply voted “present,” they would still need another Republican to support the legislation to pass it. Mr. Johnson’s office declined to clarify his stance.
With potential roadblocks in mind, Ms. Baldwin has been working it, on the phone on the weekends and anywhere she runs into a Republican as she goes about her day.
Even as the issue moved to the back burner as Democrats’ climate and health package took up the final days before the Senate’s August recess, Ms. Baldwin was working with Ms. Collins to build more support among Republicans by adding language stating explicitly that it would not take away any religious liberty or conscience protections.
Dressed in a sea-foam green jacket, she conferred quietly on the Senate floor last week with her desk mate, Senator Mike Braun, Republican of Indiana, who has said he was undecided about how he will vote on the bill. Mr. Braun, listening intently, at one point took a pen and began jotting down notes as Ms. Baldwin spoke.
As she buttonholed Senator Todd Young, Republican of Indiana, Mr. Young could be heard telling Ms. Baldwin: “Oh wow, that would be powerful,” and pondering if he could find some Congressional Research Service reports related to their discussion.
Ms. Baldwin has worked to persuade Republicans that it is safe to back the measure. She said she had reminded Senator Mitt Romney of Utah that all four of his colleagues in Utah’s all-Republican House delegation — voted “yes.”
The whipping operation started almost immediately after the House vote, when Ms. Baldwin headed to the floor to introduce the Senate version of the bill and ran into Mr. Portman.
“I had on my smartphone the names of all the Republicans who had just voted in the House, and there were a bunch of Ohio Republicans,” Ms. Baldwin recounted. “I said, ‘Rob, look at this!’”
“I started talking with others, and it went from hypothetical to, ‘We could really do this,’ ” she said.
In her conversations, Ms. Baldwin has underscored that the bill is simple — less than four pages long. She has told other Republicans that a rationale like Mr. Johnson’s — that the legislation isn’t necessary, but there’s no harm in passing it either — is a perfectly acceptable justification for a “yes” vote.
The lobbying effort has been as nonconfrontational as Ms. Baldwin is. Right after Senator Marco Rubio, Republican of Florida, dismissed the bill to a CNN reporter as a “stupid waste of time,” Ms. Baldwin found herself alone in an elevator with him. The elevator ride was described as a “confrontation” between a gay senator and a partisan warrior who is up for re-election in a red state.
But Ms. Baldwin isn’t one for heated encounters. She said she left the elevator, telling Mr. Rubio politely, “We’ll visit on this again.” (The two did, in fact, visit again on the issue, a spokesman said.)
Senator Kyrsten Sinema, Democrat of Arizona and the second openly L.G.B.T.Q. woman elected to the Senate, has also been working closely with Ms. Baldwin to rally Republican support for the bill. She spoke with Mr. Johnson on the Senate floor before Ms. Baldwin texted him, and has been working closely with Mr. Tillis and Mr. Portman, her spokeswoman said.
Ms. Baldwin said she was determined to ensure that the Senate doesn’t make the same mistake on marriage equality that she believes it did on abortion — that is, waiting until it is too late to try to legislate federal safeguards for rights that the court has already found to be protected by the Constitution.
So she was taking nothing for granted. As she counts noses, Ms. Baldwin said she has been keeping in mind the coronavirus, cognizant that in a 50-50 Senate, even one case could wipe away the margin of support needed to steer the bill to a final vote.
“We’re going to need everybody here. If we have two Democrats out with Covid, I need two more Republicans, which I may have, but you don’t want to roll the dice,” Ms. Baldwin said. “You want to be certain.”
Catie Edmondson contributed reporting from Washington.