After 20 years of marriage, Sanford filed for divorce in December.
The Fellowship also reportedly counseled another of its members, Ensign, who admitted to an affair with Cynthia "Cindy" Hampton, the wife of his former co-chief of staff Doug Hampton, in June 2009.
Doug Hampton spoke with ABC News' Cynthia McFadden in November 2009 about his boss' affair and the cover-up, revealing that he turned to the Fellowship in early 2008 to intervene. At the time, Ensign was a resident at the C Street House.
Hampton said he was not advised by the Fellowship to cover up the affair, but instead to "be cool." He said they felt they needed a more powerful voice to confront Ensign, and reached out to C Street resident and conservative leader Sen. Tom Coburn, R-Okla.
"'We need help. We're not big enough,'" Hampton said, recalling his conversation with the Fellowship. "'[Ensign] is a United States senator and so even though we're friends, we're close, we're brothers in Christ, we need power to confront this: Sen. Tom Coburn, the hit man."
Hampton said that on Valentine's Day 2008, the C Street leadership and Coburn helped him confront Ensign.
"Tom [Coburn] really kind of takes the helm," Hampton recalled. "Oh, he's smoking. He is one upset man. ... And then John kind of breaks down, [saying] 'I made a mistake, I really screwed up.'"
Coburn originally denied he was ever part of brokering a settlement. In a statement to "Nightline" responding to this story, Coburn's spokesman John Hart confirmed that he did offer to help Hampton in the negotiation, but says the conversations were "initiated by Doug, not ... Coburn."
Hampton provided "Nightline" with a letter, which he said the group at C Street forced Ensign to write and send to Cindy, ending the relationship.
"I used you for my own pleasure," Ensign wrote. "God never intended for us to do this."
According to Sharlet, the Fellowship relies heavily on the biblical narrative of King David in its teachings. Despite David's "mixed record" for adultery, he is revered because he was chosen by God for power.
Though the organization has taken steps toward transparency, the Fellowship continues to operate under the radar.