The Minnesota group pushing the proposed amendment to ban same-sex marriage is breaking from a well-tested campaign playbook, launching a more aggressive effort than past campaigns in other states.

Amid an unrelenting assault from the other side, Minnesota for Marriage attempted to wage a boycott of General Mills last week, in part to spook other companies from joining the Minnesota-based food giant in opposing the amendment.

"Each campaign is different," deputy campaign manager Andy Parrish said while standing across from General Mills' headquarters during a lunchtime rally. "You have to adapt and change."

In what is emerging as a high-stakes fight nationally, amendment supporters are refining a formula that has succeeded without exception in 31 other states, to ensure Minnesota doesn't break that streak.

With more than 18 months to prepare, marriage amendment opponents have assembled an unprecedented and well-financed campaign, vastly outraising supporters while amassing an A-list of powerful and politically collected allies that include everyone from DFL Gov. Mark Dayton to the CEO of General Mills to even some religious leaders.

Minnesota law already forbids same-sex marriage, but amendments supporters want voters to cement it into the state Constitution to prevent judges or future legislators from changing it. Opponents are waging a fierce campaign to defeat the amendment and eventually hope to legalize same-sex marriage in the state.

Minnesota for Marriage leaders are heading into the summer months with a dogged focus on keeping supporters energized and pushing back hard if other Minnesota businesses surface to oppose the amendment.

When General Mills stepped into the fray, Minnesota for Marriage immediately issued news releases that said "the Green Giant, Lucky Charms, Cinnamon Toast Crunch, Kix and Trix have all declared war on Marriage" and that the company was promoting "genderless marriage."

Parrish, a former chief of staff and top campaign staffer for Republican U.S. Rep. Michele Bachmann, said of his tactics, "If they want to come out and support one side or the other, we are going to let them know they got customers on each side."

General Mills officials later said the boycott did not hurt their business. The petition drew about 12,000 signatures nationwide, but nearly as many signed an online petition thanking the company for its stance.

Something different here

Political strategists who have watched marriage amendment fights in other states say something different is happening on both sides in Minnesota. When voters in Maine and North Carolina recently passed marriage amendments, the campaigns were not marked by high-profile boycotts or other political theater.

"In North Carolina, opponents of the amendment tried to get leading business people to speak out, but couldn't. It probably wouldn't have made any difference," said Gary Pearce, a political consultant in North Carolina. "It was all about religion. People wanted to ban gay marriage because they sincerely thought it violates their view of marriage as a sacred institution."

Minnesota for Marriage campaign manager Frank Schubert, a California strategist who has led more than 30 successful ballot initiatives, said he never counted on Minnesota being like the other campaigns.

"It's a popular myth that there's some grand plan that Frank pulls off the shelf and changes a few words here or there and now it is Minnesota," Schubert said. "The other side has been operating for a long time. They have raised a lot of money, and we expect they will vastly outspend us at the end of the day. But I have every confidence we will win."

Minnesota for Marriage says it has identified 65,000 supporters to help with the campaign. Staffers reach out daily to new church groups, which are being counted on as core support. They plan to try to draw in union members, minority communities and the elderly -- groups that tend to vote Democratic but who have often opposed same-sex marriage in other states.

Fragile coalition

In past same-sex ballot question fights, amendment supporters found that 40 percent of their votes came from Democrats. But, Schubert noted, libertarian-leaning Republicans tend to reject the marriage amendment as government intrusion. That leaves him to thread a unique and fragile coalition.

"I've spent 30 years running ballot-issue campaigns, and I know how to build coalition of people who wouldn't normally agree on the time of day," Schubert said. "Part of the reason I have been so successful is understanding that people evaluate issues in a very different way than they evaluate partisan candidates."

That's why Minnesota for Marriage has worked relentlessly to coordinate with churches and various religious groups.

Religious observers say church activity is likely to tick up by September. Supportive pastors are expected to preach on the issue, endorse the amendment, even raise money to support the measure.

Twin Cities Roman Catholic Archbishop John Nienstedt warned clergy members there should be no "open dissension" of the church's backing of the amendment.

But there are noticeable cracks in the Catholic coalition.

In May, the group Former Priests for Marriage Equality released a list of 80 former Minnesota Catholic priests against the amendment.

In May, nearly 200 Catholics from across Minnesota met in a Methodist church in Edina to discuss how they're working within their churches to defeat the amendment. At the event, the Rev. Bob Pierson, a priest at St. John's Abbey in Collegeville, said he'd be voting no on the amendment.

Minnesota for Marriage also is rallying the roughly 750,000 conservative evangelical Protestants, who have made up a formidable voting bloc in other states that passed the amendment.

The pro-amendment group Minnesota Family Council also helped sponsor a conference in May to encourage pastors to speak to congregants in support of the amendment; close to 175 pastors showed up.

The Rev. Jeff Evans, church outreach representative for Minnesota for Marriage, who heads an evangelical church in Minnetonka, says the group is booked at churches throughout the summer and he expects the pace to pick up by the fall.

In the meantime, amendment supporters say they will rewrite the playbook any way necessary to win.

"It's my goal never to lose," Schubert said. "And we are never going to give up."

Baird Helgeson • 651-925-5044