"There are roughly 350,000 congregations in the United States, and many of them do great work: feeding the hungry, clothing the poor," John Oliver says, opening his latest Last Week Tonight report. "But this is not a story about them. This is about the churches who exploit people's faith for monetary gain."

As Oliver explains, "televangelism is still thriving in this country," with preachers like Robert Tilton using the "prosperity gospel" to squeeze out mind-boggling amounts of money from their impressionable audiences. One televangelist, Creflo Dollar, used a fundraiser to buy a $65 million jet,...