ST. PAUL, Minn. » In March 2004, with Massachusetts soon to allow gay couples to wed, Michele Bachmann delivered a dire warning to her fellow Minnesotans: The children of their state were at risk.

"We will have immediate loss of civil liberties for five million Minnesotans," Bachmann, then a state senator, told a Christian television network as thousands gathered on the steps of the Capitol to rally for a same-sex marriage ban she proposed. "In our public schools, whether they want to or not, they’ll be forced to start teaching that same-sex marriage is equal, that it is normal and that children should try it."

Now that she is seeking the Republican presidential nomination, Bachmann, a Minnesota congresswoman, is talking more about federal spending than about gay rights. But her political rise has its roots in her dogged pursuit of an amendment to the state constitution prohibiting same-sex marriage — "her banner issue," said Scott Dibble, a Democratic state senator who is gay — and her mixing of politics with her evangelical faith.

The "Bachmann marriage wars," as Dibble calls that legislative debate, offer a case study in the congresswoman’s ability to seize an issue and use it to circumvent the party establishment — the same tactic, analysts say, that made her a Tea Party star in Washington and a hot commodity on the campaign trail.

"That’s her recipe: Find the issue, then use it politically to mobilize previously marginalized or disconnected groups," said Lawrence Jacobs, a political scientist at the University of Minnesota. "For those of us who followed her from the beginning, it’s like reading a romance novel with a formula."

Bachmann’s strong stance on homosexuality — she once likened it to "personal bondage, personal despair and personal enslavement" — and her anti-abortion views have appeal for some Republican primary voters. In Iowa this month, she delighted conservatives by signing a pledge opposing "any redefinition of marriage." (Her fellow Minnesotan and presidential rival, Tim Pawlenty, a former governor, was left explaining why he did not.)

Yet her position has also become a distraction for her campaign, drawing critics and subjecting her family to the kind of scrutiny once reserved for the relatives of nominees. It has exposed a longstanding rift between the congresswoman and her stepsister, who is a lesbian. It has also raised questions about whether her husband, Marcus, who runs two Christian counseling centers, practices "reparative therapy," or gay-to-straight counseling, derided by critics as an effort to "pray away the gay."

For the Bachmanns, the issue is entwined with faith. Until recently, they were members of Salem Lutheran Church in Stillwater, part of the Wisconsin Evangelical Lutheran Synod, which holds that "a believing member" cannot "remain a practicing homosexual in defiance of God’s word." Friends say they now attend services at another evangelical church, Eagle Brook, closer to their new home in another Stillwater neighborhood.

"They are absolutely not against the gays," said one close friend, JoAnne Hood, who also attends Eagle Brook. "They are just not for marriage."

Same-sex marriage was not much of an issue here when Bachmann, who declined to be interviewed, arrived at the statehouse as a new senator in January 2001. Minnesota had already enacted its own version of the federal Defense of Marriage Act, which defines marriage as between a man and a woman for legal purposes.

Then, in November 2003, the Massachusetts Supreme Court declared that state’s law banning same-sex marriage unconstitutional. Bachmann sprang into action.

"She was holding press conferences and saying, ‘We can’t have that in Minnesota,"’ said Don Betzold, a Democrat and a former chairman of the state Senate Judiciary Committee. She vowed to introduce a constitutional amendment and, seemingly overnight, emerged as Public Enemy No.1 to Minnesota’s gay rights advocates, who were alarmed by her word choice and her intensity.

Stephen E. Dille, a retired Republican state senator who says Bachmann was known more for "giving peppy speeches" than getting legislation through, said the marriage amendment was "awkward" for the caucus because one Republican senator was gay. Others saw the issue as political loser in a state known for tolerance.

But Christian conservatives embraced it — and Bachmann.

"She stood up as a Christian," said Bob Battle, pastor of the Berean Church of God in Christ here. "She made her point of view known, and she gave Christians a voice."

She proved herself an extraordinary organizer. "The social conservative groups were largely isolated; she went to them and made a very hard-edged argument that their deeply felt values were being ignored," Jacobs said.

In the end, the Bachmann amendment faltered. The Minnesota House, controlled by Republicans, adopted it. Pawlenty made brief appearances at two of the marriage rallies — a nod to how Bachmann had managed to elevate the issue. Bachmann rose through the ranks to briefly become assistant minority leader, a position she later lost in a dispute with the Republican leadership.

But her bill stalled in the Senate, controlled by Democrats. In 2006, in the waning days of the legislative session — her last in St. Paul — she tried to revive it.

"She brought in a whole bunch of people that were going to be at the Capitol around the clock," said Betzold, the former Judiciary Committee chairman. "Kids were sleeping on marble floors, trying to pressure us to bring the bill up in the closing hours."

Her tenacity earned her a shot at a job in Congress. In 2006, Bachmann loyalists turned out in droves to help her leap over more senior Republicans to grab the party’s nomination for the seat she now holds.

In Washington, Bachmann has again found herself at odds with the party establishment, this time as head of the House Tea Party Caucus, which she founded. Some Republicans gritted their teeth when Bachmann gave her own televised rebuttal to President Barack Obama’s State of the Union address; the party had picked Rep. Paul D. Ryan of Wisconsin to give the official response.

Bachmann has not been a leader in Washington on same-sex marriage, but has co-sponsored four resolutions opposing it. Here in St. Paul, though, her advocacy seems to have had a lingering effect. A constitutional amendment barring gays from marrying will be on the Minnesota ballot in 2012.