In early 2012, a public policy poll found that 50 percent of Minnesotans surveyed favored a constitutional amendment to ban gay marriage, and only 40 percent said they opposed the amendment.

The amendment, of course, was defeated, and the Minnesota Senate is expected to vote to legalize gay marriage this week.

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The vote in the Minnesota House wasn’t even close — 75-59 with four Republicans voting in favor.

So what happened? It all began when a backlash against the Marriage and Voter ID amendments were widely credited with helping sweep Democrats into controlling both legislative chambers in the November election.

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The high-powered Minnesota United For All Families that guided the “Vote No” campaign fell seamlessly behind the push for legalization. At the same time, legislators in other states, from Maine to Washington, approved legalization.

Polls continue to show younger voters overwhelming support for gay rights. While even a few months ago Minnesota legislators expressed skepticism a legalization effort would succeed, the measure seemed to acquire an organic momentum of its own.

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Somehow this issue has taken center stage, and an air of inevitability has changed places with uncertainty, as Minnesota appears poised to legalize gay unions.