Herman Cain's call for an investigation into President Barack Obama's decision to no longer defend a federal ban on gay marriage has riled the National Organization for Marriage (NOM).

The Republican presidential candidate said during a conference call with reporters last week that the Obama administration's position to no longer defend in court the Defense of Marriage Act (DOMA), the law that forbids federal agencies from recognizing the legal marriages of gay and lesbian couples, was an impeachable offense.

“That's a great question and it is a great – it would be a great thing to do but because the Senate is controlled by Democrats we would never be able to get the Senate first to take up that action, because they simply don't care what the American public thinks. They would protect him and they wouldn't even bring it up,” Cain said.

He added: “So the main stumbling block in terms of getting him impeached on a whole list of things such as trying to pass a health care mandate which is unconstitutional, ordering the Department of Justice to not enforce the Defense of Marriage Act – that's an impeachable offense right there. The president is supposed to uphold the laws of this nation … and to tell the Department of Justice not to uphold the Defense of Marriage Act is a breach of his oath. … There are a number of things where a case could be made in order to impeach him, but because Republicans do not control the United States Senate, they would never allow it to get off the ground.”

NOM, the nation's most vociferous opponent of gay marriage, chided Cain, saying he needed to “pledge to actions, not just words on marriage.”

“We need someone who does not just talk the talk, but walks the walk on marriage. That's why we asked all the GOP candidates to sign NOM's 5-point marriage pledge. [Minnesota Rep. Michele] Bachmann, [former Pennsylvania Senator Rick] Santorum, and [former Massachusetts Governor Mitt] Romney have. Why hasn't Herman Cain?” asked Maggie Gallagher, board chair of NOM, in a blog post.

“President Obama claimed he supported traditional marriage but then failed to follow through. If Herman Cain wants to distinguish his position from President Obama, he should commit to concrete actions, not just rhetoric in support of marriage,” she added.

Candidates signing NOM's pledge promise to support a federal constitutional amendment banning gay marriage, defend the Defense of Marriage Act (DOMA) in court, appoint judges and an attorney general who will “respect the original meaning of the Constitution,” appoint a presidential commission to investigate the “harassment of traditional marriage supporters,” and back legislation that would allow a ballot question on the issue for voters of the District of Columbia.