JOHNSTON, Iowa — A key Senate leader standing in the way of efforts to bring a proposed constitutional amendment to ban same-sex marriages before Iowa voters said Friday he understands the potential political consequences.

“I’m willing to accept the possibility of me losing,” said Senate Majority Leader Mike Gronstal, D-Council Bluffs, who has steadfastly opposed the marriage amendment effort.

“I accept that every vote I take up in that chamber can result in my defeat in the next election. It can result in a defeat by my fellow members to be their leader. I accept that reality,” Gronstal said during Friday’s taping of Iowa Public Television’s “Iowa Press” show. “I think you’ve got to stand for something in politics.”

Gronstal’s stance has prompted Republican Gov. Terry Branstad — who favors a referendum on the marriage issue — to refer to him as “a dictator.” Minority Republicans who tried unsuccessfully to force a vote Thursday through procedural maneuvering called him an obstructionist and likened the Senate to Gronstal’s monarchy. Conservative activists have indicated they will work to defeat Gronstal in next year’s Senate District 50 race.

The marriage resolution has been introduced in the Senate by Republicans, but has never come up for a vote in committee. If it should make it to the debate calendar this session, Gronstal has indicated he will exercise his prerogative as floor leader not to allow a Senate debate.

Some opponents contend several members of the 26-member Democratic majority have stated publicly that they favor defining marriage as only between one man and one woman.

Gronstal, who served one term in the House and is in his seventh term as a senator, acknowledged that he worries about politics in his home district and campaigns hard to get re-elected. He said everybody within the Senate Democratic caucus has to make their own calculation about how they will campaign and win their races but he added, “I don’t give up what I believe in” in taking a position that some Iowans may not agree with.

In the Iowa House, majority Republicans have indicated they expect to debate a resolution next week calling for a constitutional amendment declaring “marriage between one man and one woman shall be the only legal union valid or recognized in this state.”

For constitutional amendments to come before a vote of the people, both the House and Senate must pass the exact same language in two consecutive general assemblies, which would mean the earliest the matter could come before voters would be in the 2014 election unless it was handled by a special election. If approved by voters, the constitutional amendment would undo an April 2009 Iowa Supreme Court decision that ruled a state law unconstitutional that defined marriage as only between one man and one woman, which paved the way for civil marriages between couples of the same gender in Iowa.