Minnesota's expected move this week to legalize same-sex marriage might be seen by future historians as the next logical, predictable step in the GLBT rights movement's progression in America.

This, after all, is the Midwestern state most culturally akin to New England. After Rhode Island on May 2 became the last of the six New England states to offer same-sex couples the chance to obtain a marriage license, it's understandable to think that Minnesota would be next.

Delaware got ahead of Minnesota last week. Illinois is hard on its heels. But if, as expected, the Senate on Monday follows the lead of the House's 75-59 vote on Thursday, Minnesota will be the first Midwestern state to "do it the New England way" — that is, to extend full marriage rights to same-sex couples via legislative vote, not judicial order. (Iowa's 2009 legalization came at the hands of the courts.)

Minnesota's historic and cultural connection with New England is hard to overstate. That became clear to me when I inspected a lot of 19th-century Minnesota census records a few years ago. The most frequently cited birthplaces on those lists weren't Norway, Sweden and Germany. They were New Hampshire, Maine, Massachusetts and Vermont.

The New Englanders who populated Minnesota in those years were folks who knew how to turn running water into money. That's what brought them here. They were also town-meeting Congregationalists who prized equality under the law, valued the citizenship of all men (women were another story, for another day) and wouldn't abide any king or bishop telling them how to conduct their personal affairs.

A line can be drawn from those ideas to the case made on the House floor last week that Minnesota law ought not treat same-sex couples differently from the other kind.

But I can draw a shorter, more direct line to explain how Minnesota finds itself on the verge of becoming the 12th state in the nation to grant same-sex couples the chance to legally marry. My line traces from the decision by the 2011 GOP-controlled Legislature to put a constitutional amendment banning same-sex marriage on the November 2012 ballot.

If politics were scored like tennis, that was an "unforced error."

Marriage-ban amendments had served Republicans well in 30 other states, boosting GOP turnout as voters put them into state constitutions. When both legislative chambers went Republican in 2010, the new majorities couldn't wait to let the marriage issue work its partisan magic here.

They didn't foresee that thousands of ordinary Minnesotans, gay and straight, were willing to work some magic of their own to keep the amendment out of Minnesota's charter.

GLBT Minnesotans began acknowledging their sexuality in big numbers a generation ago. But not many talked openly about how the unavailability of legal marriage hurt them, their partners and their children until the amendment threatened to put marriage even further out of reach. Last year, with the encouragement of a strategically smart Minnesotans United for All Families campaign, up-close-and-personal conversations about the implications of marriage law unfairness happened all over this state.

Asking Minnesotans to say a constitutional "no" to same-sex marriage perversely hastened the day when, via their elected representatives, they would say "yes."

Last week, I played my favorite postmortem game, "What If," with a senior Republican legislator who would play only if I wouldn't print his name.

What if the GOP had not advanced the amendment? He agreed with me that Minnesota today likely would not be on the verge of legalizing same-sex marriage. That move might still be coming, but not this year.

Then he offered a variation: What if the amendment had been accompanied by a move to allow "civil unions," the not-quite-marriage legal status that Red Wing GOP Rep. Tim Kelly offered on the House floor Thursday as an alternative to full legalization? My GOP game-mate speculated that if Republicans had simultaneously made civil unions available to same-sex couples, the marriage ban might have passed muster with the voters.

On Thursday, Kelly's amendment went down on a 22-111 vote Thursday. Its time had come and gone. Now that the issue has been made personal to fair-minded Minnesotans, nothing short of full equality will do.

Lori Sturdevant is a Star Tribune editorial writer and columnist. She is at lsturdevant@startribune.com.