Wait—what's the joke?

An admirer of William Trevor, the often-bleak Irish author — a taste Mr. McCain has picked up — Mr. Salter is known among colleagues for his gloomy view of human nature and the world. Mr. McCain has a similar streak. “It’s always darkest before it’s totally black,” he often says, a motto borrowed from the “Peanuts” character Charlie Brown that he jokingly misattributes to Mao. —NYT