Former Massachusetts Gov. Mitt Romney (R) won't sign a social issues pledge a prime social conservative in Iowa has said would be key to his endorsement.

Romney's campaign said he wouldn't sign "The Marriage Vow," a manifesto opposing same-sex marriage and promoting other socially conservative values put forth by Bob Vander Plaats, the president and CEO of the Iowa-based group The Family Leader.


"Mitt Romney strongly supports traditional marriage but he felt this pledge contained references and provisions that were undignified and inappropriate for a presidential campaign," said Romney spokeswoman Andrea Saul.

The pledge has been criticized in some quarters for its various vows, but also for its original provision including a preamble suggesting that African-American families were more stable under slavery than they are today. (That measure has since been stricken from the pledge.)

Former Sen. Rick Santorum (R-Pa.) and Rep. Michele BachmannMichele Marie BachmannGillibrand becomes latest candidate scrutinized for how she eats on campaign trail Trump will give State of Union to sea of opponents Yes, condemn Roseanne, but ignoring others is true hypocrisy MORE (R-Minn.) have signed the pledge, though they've been forced to explain their association with the pledge.

"I just want to make it absolutely clear: I abhor slavery," Bachmann said Tuesday evening on Fox News. "And under no circumstances would any child be better off growing up under slavery. But that isn't what I signed; that isn't what I believe."

Romney's decision not to sign the pledge might have little effect on his campaign, as he's dedicated little effort to winning Iowa's caucuses, especially compared to his effort in the Hawkeye State in 2008. But a supporter in Iowa came to his defense nonetheless.

"One of the reasons I support Governor Romney is his support for traditional marriage. However, I am glad he won't sign this ill-advised pledge," said Cedar Rapids state Rep. Renee Schulte (R). "The Family Leader would do more to advance the issues that conservatives like Mitt and I support if they kept it simple."

Vander Plaats sought to rebut critics in a Web video.

"Some of my critics and some of The Family Leader's enemies, they're going to say that [we're claiming that] raising children back in the time of slavery is better," he said. "That is absurd."

More broadly, this is the second pledge on social issues that Romney's refused to sign. He didn't join signatories to an anti-abortion-rights pledge proposed by the Susan B. Anthony List because he said it was overly broad and would have unintended consequences.

Romney has signed the Americans for Tax Reform "Taxpayer Protection Pledge" and the "Cut, Cap and Balance" pledge favored by Sen. Jim DeMint (R-S.C.). Both have more to do with fiscal issues and the economy, an area on which Romney's focused his campaign this cycle.

Romney isn't the only Republican presidential candidate to reject the pledge. Former House Speaker Newt Gingrich (R-Ga.) has said he wouldn't sign it, and Minnesota Gov. Tim Pawlenty (R), who's heavily courting Iowa voters, hasn't said whether he would sign the pledge.