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The Respect for Marriage Act, which passed the Senate Tuesday in a 61-36 vote, has been introduced in Congresses since 2009.
The overturn of Roe v. Wade in June and the record-shattering number of bills introduced this year that target LGBTQ rights likely contributed to the measure's relative success this year, policy experts said.
Support for same-sex marriage has also increased drastically over the last decade, with more than 70 percent of Americans polled by Gallup this year in agreement that same-sex unions should be legally valid.
Iterations of the Respect for Marriage Act have been introduced in at least five Congresses since 2009, though up until now, prior versions of the bill to enshrine marriage equality into federal law have struggled to gain enough bipartisan support to advance through both the House and Senate.
With the current Respect for Marriage Act's passage all but assured, policy experts say the measure's success this year - during which the Supreme Court discarded long-standing federal abortion protections and state lawmakers introduced a tidal wave of legislation checking the rights of LGBTQ Americans - is by no means a coincidence.
More than 300 pieces of legislation targeting LGBTQ identities were introduced in state legislatures across the country over the last year - a sobering record that has made non-LGBTQ people more aware of attacks and hostility against the community, Cathryn Oakley, state legislative director and senior counsel at the Human Rights Campaign, a leading LGBTQ rights group, told The Hill.
"People have seen how mean-spirited a lot of that rhetoric has been," Oakley said.
But the most compelling difference "is absolutely the Dobbs decision," Oakley said, referring to Dobbs v. Jackson Women's Health Organization, the June Supreme Court ruling that struck down Roe v. Wade, which had protected the constitutional right to abortion since 1973.
"The Dobbs decision was so regressive and so astonishing that to many people, it really shook loose this idea that we can be complacent," Oakley said. "That is the single-most significant reason for the Respect for Marriage Act moving forward right now."
Sen. Tammy Baldwin (D-Wis.), who led the charge to pass the measure in the Senate, told The Hill on Tuesday that support for the bill this time around has largely been driven by a recognition that the constitutional and legal grounds on which Roe was decided are strikingly similar to those of other landmark decisions including Loving v. Virginia, which legalized interracial marriages in the U.S., and Obergefell v. Hodges, which legalized same-sex unions.
Justice Clarence Thomas following the fall of Roe suggested the high court revisit its 2015 same-sex marriage ruling, which he and fellow Supreme Court Justice Samuel Alito have claimed has had "ruinous consequences for religious liberty."
"People in both interracial and same-sex marriages are very concerned about the security of their marriages and the certainty of their marriages moving forward," Baldwin said. "There was tremendous shock - both in Congress and the public at large - to see Roe v. Wade overturned."
Baldwin, who in 2012 become the first-ever openly gay person elected to the Senate and is currently one of just two out LGBTQ legislators in the upper chamber, added that Congress is better primed to pass the Respect for Marriage Act this year because attitudes around LGBTQ couples and rights have shifted drastically over the last decade.
Support for marriage equality among American adults shot to all-time high this year in an annual Gallup poll, with more than 70 percent in agreement that marriages between same-sex couples should be recognized as legally valid.
In 2009, when the Respect for Marriage Act was first introduced by Rep. Jerry Nadler (D-N.Y.), just 40 percent of Americans polled by Gallup said same-sex married couples should have the same rights as those in "traditional" heterosexual marriages.
Support for same-sex marriage equality reached majority level in 2011, when the second iteration of the bill was brought up by Nadler and Sen. Dianne Feinstein (D-Calif.), and climbed to 60 percent in 2015, the year Obergefell was decided.
Nadler and Feinstein introduced a third version of the Respect for Marriage Act in 2013 and attempted to pass the bill for a fourth time in 2015. Same-sex marriage support has risen steadily since then, according to Gallup.
"In the years after Obergefell was decided, more and more of my colleagues have family members, friends and staff members who are in same-sex marriages," Baldwin told The Hill, adding that as public support for marriage equality continues to grow, "senators are moving in that direction, too."
Sen. Rob Portman (R-Ohio), one of the Respect for Marriage Act's sponsors in the Senate, in 1996 voted in favor of the Defense of Marriage Act (DOMA) that defines marriage for federal purposes as a union between one man and one woman.
Portman credits his shifting views on marriage equality to his son, Will, who came out as gay in 2011. In 2013, Portman became the only sitting Republican senator at the time to publicly back legal same-sex unions.
"It's a change of heart from the position of a father," he told reporters at the time.
The Respect for Marriage Act would officially repeal DOMA - a portion of which was ruled unconstitutional by the Supreme Court in 2013 - and require each state to recognize same-sex marriages as valid if those unions were performed in a state where they are legal.
State-level bans on same-sex marriages remain on the books in more than 30 states but are unenforceable under protections established by the Obergefell ruling.
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