New GOP frontrunner Newt Gingrich has signed a pledge from Iowa social conservative group The Family Leader that forbids committing adultery, according to the political blog The Iowa Republican.

The pledge has already been signed by Texas Governor Rick Perry, Rep. Michelle Bachmann (R-MN) and Rick Santorum. Former Massachusetts Governor Mitt Romney and Rep. Ron Paul (R-TX) have said they would not sign the pledge.

Gingrich chose to sign today after initially declining to do so in August, when the text of the pledge claimed that African-American children were better off under slavery than they are today. That text has since been removed. He also vowed to uphold The Defense of Marriage Act (DOMA), which prohibits same-sex marriage.

"I also pledge to uphold the institution of marriage through personal fidelity to my spouse and respect for the marital bonds of others," he wrote in a letter to The Family Leader. "I will also aggressively defend the constitutionality of DOMA in federal and state courts. I will support sending a federal constitutional amendment defining marriage as the union of one man and one woman to the states for ratification."

Gingrich is currently married to his third wife Callista, who he married after cheating on his second wife while she struggled with a diagnosis of multiple sclerosis. He divorced his first wife to marry his second, his mistress at the time, presenting her with papers the day after she had surgery for uterine cancer.