A national group that has spent millions to defend the traditional definition of marriage is pledging $500,000 to "take out" any Minnesota Republican legislator who votes to legalize same-sex marriage.

The National Organization for Marriage's announcement comes less than a week after Republican state Sen. Branden Petersen of Andover said he was considering becoming a co-sponsor of a proposal to legalize same-sex marriage in Minnesota. A legalization bill is expected to be introduced later this week, touching off what is likely to be one of the most divisive issues at the Capitol this year.

"Republicans like Branden Petersen don't realize that not only is voting to redefine marriage a terrible policy, it is also a career-ending vote for a Republican," said Brian Brown, president of the National Organization for Marriage. "NOM will do everything in our power to defeat any Republican who votes in favor of same-sex marriage."

The increasingly public fight over the marriage issue is revealing a growing fracture within the state Republican Party.

"The Republican Party is split on gay marriage," said Pat Anderson, a former Republican National Committeewoman who is now interim GOP chairwoman of the Fourth Congressional District. "That's part of the big fight within the party, between small government, liberty conservatives versus traditional conservatives."

'My vote cannot be bought'

At the urging of socially conservative donors, the GOP-controlled Legislature voted nearly two years ago to put on the ballot a proposed constitutional amendment to define marriage in strictly heterosexual terms, as the union only of a man and woman. Minnesota voters rejected that amendment and also handed control of the Legislature to Democrats, dramatically reshuffling the marriage issue at the Capitol. Now some Republicans like Petersen are publicly bucking what had been a nearly lockstep party orthodoxy against same-sex marriage.

"Whether they spend $500,000 or $5 million, it is not going to make any difference in my decision, either way," Petersen said Monday. "My vote cannot be bought."

Some Republicans who oppose same-sex marriage say they appreciate the National Organization for Marriage taking such a strong position. The group spent more than $2.2 million in its effort to pass the marriage amendment and has been a driving force in marriage-related measures around the country.

"They have deep pockets and they will use the tools they can," said state Sen. Warren Limmer, a Maple Grove Republican who sponsored the marriage amendment. "I don't think it's just bluster. They are in it for the long haul and put their money where their mouth is."

Several Republicans said Limmer's socially conservative wing of the party is dwindling, replaced increasingly by younger, more libertarian members who either support same-sex marriage outright or say the government should not be involved.

Anderson said she has four college-age children, "and every one of them is Republican and every one of them worked against the marriage amendment."

State GOP won't punish

The head of the Minnesota Republican Party said the party is steering clear of the fight and does not plan to punish legislators who vote for same-sex marriage.

Local activists will decide the fate of GOP legislators, said Pat Shortridge, chairman of the Minnesota Republican Party.

"I'm sure the candidate's views on marriage will come up, but so will their views on taxes, spending, regulation, health care, education, life, the Second Amendment, and a host of other important issues," he said.

That doesn't mean outside groups won't be influential in coming years.

The National Organization for Marriage noted that it helped "take out" three of four New York GOP senators who voted to legalize same-sex marriage in that state "by repeatedly informing their constituents of their betrayal on marriage."

"We will not hesitate to do the same thing in Minnesota," Brown said.

Minnesotans United, the group leading the effort to legalize same-sex marriage, said the National Organization for Marriage has not always followed through on threats to oust legislators who oppose its views. Same-sex marriage supporters said the vast majority of legislators who voted to legalize same-sex marriage in other states were re-elected.

"Statistics show that nearly every legislator who stands up for the basic freedom to marry — like Senator Petersen — is rewarded for their leadership with re-election," said Richard Carlbom, campaign manager for Minnesotans United.

Baird Helgeson • 651-925-5044