Maxine Waters photo by AP. Illustration by Mike Sullivan

On Wednesday, Facebook CEO Mark Zuckerberg will face a grilling by a congressional committee led by Maxine Waters. That was supposed to be Sheryl Sandberg's job. 

Initially, Sandberg, Facebook’s chief operating officer, was scheduled to testify before the committee about the company’s Libra cryptocurrency, but when she had a private meeting with Waters on Capitol Hill earlier this month, the conversation turned testy. Sandberg repeatedly said she wasn’t a Libra expert and recommended adding David Marcus, the Facebook executive who helped create Libra, to the witness list, according to a person familiar with the meeting.