Marriage equality advocates are understandably disappointed by Senate Judiciary Chairman Patrick Leahy’s decision not to pursue an amendment to the immigration reform bill that would have recognized same-sex relationships. Announcing his decision “with a heavy heart,” Leahy conceded that pursuing the amendment could jeopardize the bipartisan coalition around immigration reform.

But few issues have ever evolved so quickly, and advocates should not take this week’s setback as the last word on equality. For clues on what could happen to the GOP’s trajectory on same-sex marriage in the next few years, Canada’s experience could prove enlightening. Canada’s Conservative Party, which came to power with a formal platform opposing same-sex marriage, has made a remarkable 180 in just a few short years. Here’s how it happened.

Canada was governed by the center-left Liberal Party when discrimination in marriage was ended there in 2005. But in 2006, power shifted to the Conservative Party, which formally opposed same-sex marriage and took a host of other positions that were quite right-wing by usual Canadian standards.

As in some U.S. states, marriage equality had first been required by rulings from courts, up to and including the Supreme Court of Canada. But unlike in, for instance Massachusetts, this was not the end of the story, since a unique provision of the Canadian Charter of Rights and Freedoms allows provincial legislatures and the national parliament to enact a law notwithstanding a ruling by the courts.

This “notwithstanding clause” has rarely been invoked, but ever since ever since coming to power in 2006, the Conservatives have had the option to try to use it to reverse marriage equality. Instead, though, they have mostly avoided the issue. In order to follow up on a campaign promise, Prime Minister Stephen Harper brought the issue of same-sex marriage before parliament in late 2006. But he permitted a “free vote” that allowed party members to vote their consciences rather than any specific party line. The motion failed 175-123, and since then, the Conservatives have made no further efforts to uproot marriage equality. In 2011, the issue went unmentioned in their party platform . A complicated legal ruling about same-sex divorce in 2012 could easily have provided a pretext to reopen the question, but instead the Conservatives quietly resolved it in a way that strengthens marriage equality.

And the changes go farther still. A remarkable 2012 article in the right-leaning National Post claimed that the Conservatives have in fact become “warriors for gay rights,” and detailed a broad range of pro-LGBT stances taken by Conservative politicians. The Immigration Minister has actively supported gay refugees from Iran, and has included LGBT people in citizenship brochures as evidence of the nation’s commitment to diversity. The Foreign Affairs Minister has condemned the perpetuation of anti-sodomy laws in African and in Caribbean countries, as well as policies in Russia that ban gay pride events. The Prime Minister has spoken out against proposals for harshly homophobic criminal laws in Uganda. After the suicide of a gay teen in Ottawa, several Conservative MPs appeared as part of an “It Gets Better” video. And Conservatives provided the decisive margin of support for a bill to protect transgender people.

Why such a shift in just the few years since 2006, and what might it suggest for the future direction of the Republican Party?

One part of the answer is electoral. Like the Republicans, Canada’s Conservatives have a lock on “traditional values” voters. Five parties currently hold seats in the Canadian House of Commons — and four of these are to the left of the Conservatives. Therefore the Tories were free to reach out to moderates in order to build a solid working majority – a situation similar to that of the Republicans.

However, another important explanation for the shift among Canada’s Conservatives is that they’ve been the party in control of government during a time of great ferment around LGBT issues. While in opposition, it is easy to criticize and pontificate. But once in government, the Tories have again and again been forced to take a stand on the full range of national and international LGBT issues. Repeatedly, they have been confronted with how to represent the demands of their voters and the values of their nation, and their conclusion seems clear. The circumstances call to mind Democrats during the Kennedy and Johnson administrations who were finally forced by the Civil Rights Movement to confront segregation. After years of ambivalence, the national Democratic Party decisively cast its lot on the side of equality in the early 1960s.

There are reasons to believe that the Republicans will hold out on this issue longer than the Conservatives. First off, they have a much larger right-wing electoral base than their Canadian compatriots, including a far more active element of the “religious right.” Also, candidates in Canadian elections are chosen by a small group of party leaders and organizers rather than by voters through primary elections. Thus they face no real threat of being “primaried” from the right, as the Tea Party has done to the moderate Republicans.

Still, the broader pattern of both public opinion and public policy in the U.S. has been following much the same trajectory as it did in Canada – – just with a delay of more than a decade. As early as 1999, a majority of poll respondents in Canada supported same-sex marriage, a dozen years before the first polls revealed a majority of Americans doing so. In both countries, levels of support were strongly skewed towards younger cohorts, suggesting the inevitability of change. As with other issues, such as decriminalizing marijuana and providing universal health care, U.S. public opinion and public policy on marriage equality has slowly and haltingly, but clearly, been following the path earlier set by Canada.

Having crossed the Rubicon of same-sex marriage, Canada’s right-wing party has been able to reach a new level of respect and support for the rights of LGBT people worldwide. So, might the U.S. right-wing party evolve to the same position? Might a future Republican president even mirror the sentiments of U.K. Prime Minister David Cameron, who in the 2011 keynote address at his Conservative Party’s annual conference declared that: “I don’t support gay marriage despite being a Conservative. I support gay marriage because I’m a Conservative.”

Right now, that day does not seem very close for the G.O.P. But on the accelerated timetable of same-sex marriage, “some day” has often turned out to come surprisingly soon.

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Raymond A. Smith

Raymond A. Smith a Senior Fellow at the Progressive Policy Institute, teaches political science at Columbia and NYU and is an investigator in the Division of Gender, Sexuality, and Health at the Columbia University Medical Center. He is the author of Importing Democracy: Ideas from Around the World to Reform and Revitalize American Politics and Government and editor of The Politics of Sexuality.