"I didn't believe it was him, of course," McCain said.
"She thought it was a prank call," said Affleck.
But last month, the political odd couple of a Hollywood actor and wife of a former Republican presidential nominee traveled to Africa together, and now they're teaming up to bring attention to the intense suffering of the Congolese people and how Americans can make a difference.
On Tuesday, McCain and Affleck will testify together about the issue on Capitol Hill, but ahead of their testimony, the pair sat down together today with ABC's Jake Tapper to discuss their recent trip to Congo and the simple steps that they say could change lives there.
"Politics doesn't have anything to do with this. This is about human lives," McCain said.
Watch Jake Tapper's interview with Affleck and McCain tonight on "ABC World News with Diane Sawyer" and "Nightline." And watch them live Tuesday on "Good Morning America."
Affleck, who first traveled to Congo five years ago, said there's a moral responsibility to pay attention to the suffering there and to get involved.
"People are dying, really dying and have been for a long time," Affleck said. "Fifteen years, three-plus million people have died. I don't know that I can make any more argument about why you should pay attention to this."
Affleck and McCain said there's a need for a special advisor to the region who can coordinate the efforts of governments and western aid organizations.
"It doesn't need a giant check," Affleck said. "It needs someone to help shepherd this process along."
Affleck's multi-million-dollar non-profit organization, the Eastern Congo Initiative, has backing from philanthropic figures like Howard Buffett, son of investor Warren Buffett. So far it has helped to fund schools and even a radio station that broadcasts programs by women. One of the biggest challenges in Congo is changing a culture that tolerates widespread sexual abuse, Affleck said, adding that in parts of the country, two out of three women have been raped.
"A way of getting underneath that and trying to uproot that is for people to hear women's voices," Affleck said. "These women, they're Congolese women who do this radio show ... they also go out into the field, into the bush, and they hand out these tape recorders, and they get these women who live in these villages to record their own kind of shows and comments."
Affleck and McCain traveled to the Congo in February, visiting local organizations that are funded by the Eastern Congo Initiative and meeting the people that they're working to help.
One of the women they met, "Christine," was kidnapped at age 14 by a militia and raped. She became pregnant, and after serious medical complications, she was taken in by Heal Africa, a hospital that receives grants from Affleck's non-profit. Seven surgeries later, she's beginning to recover.
"She's an important example," said Affleck. "She's a great, inspiring, you know, beautiful young woman."
"Her story is not unlike so many other stories that I've heard or seen," said McCain, who has been involved in Congo since 1994. "These people have such incredible spirit."
With her years of experience in the country, McCain said she was at first skeptical about Affleck, fearing that he was like other celebrities that she'd seen who drop in to Africa for what she called a "parachute photo op."
"My past experiences with other folks in the same, perhaps, arena have not been good. It hadn't been heartfelt. It hadn't been, what I believe, truly committed to the issue and the people," McCain said.
But Affleck, she said, has done the hard work of learning the issues on the ground in detail.
"This has been not only a wonderful opportunity but a wonderful treat," she said. "Ben has a working knowledge of this region. He not only understands the issues, but he understands what we need to be doing."
And Affleck added that while the Democratic actor and the Republican political wife may be separated by a partisan divide, the two have found plenty of common ground on Congo, family and even politics.
"I'd say we have, actually, frankly, quite a bit in common. I don't know if, maybe she doesn't want me to say that out loud," Affleck joked.
Watch "World News with Diane Sawyer" and "Nightline" for more tonight. And watch them live Tuesday on "Good Morning America."