The toughest moment for any candidate in Wednesday's free-for-all Democratic Presidential Debate came when Massachusetts senator Elizabeth Warren and former vice president Joe Biden publicly challenged former New York City mayor Michael Bloomberg to release women who had worked for him and complained of harassment or gender bias from the non-disclosure agreements they'd signed. It was a harsh lesson for any company leader who's ever pressed such an agreement on a complaining employee.

It began with a question from NBC correspondent Hallie Jackson about Bloomberg's known history of making sexist or sexually charged remarks, such as telling a female employee, "I would do you in a second." Bloomberg responded earnestly, "I have no tolerance for the kind of behavior that the #MeToo movement has exposed," and that at Bloomberg L.P., any such allegations are swiftly investigated and acted on, if warranted. He then went on to talk about how many women he has in his employ -- an unsatisfactory response for anyone who cares about sexual harassment or discrimination in the workplace. After all, Harvey Weinstein employed a lot of women too.

Not surprisingly, the other candidates wouldn't let him get away with it. "I hope you heard what his defense was: 'I've been nice to some women,'" Warren shot back. And then she went in for the kill. "He has gotten some number of women -- dozens, who knows? -- to sign non-disclosure agreements both for sexual harassment and for gender discrimination in the workplace. So, Mr. Mayor, are you willing to release those women from those non-disclosure agreements, so we can hear their side of the story?"

Bloomberg, who really should have been prepared for this question, stood there looking blankly at the camera for a few seconds. "We have a very few non-disclosure agreements," he finally said. "None of them accuse me of doing anything other than maybe they didn't like a joke I told." The crowd actually booed him for that line.

Warren and Biden pressed Bloomberg to release women who'd signed NDAs from those obligations then and there, onstage. "It's easy. All the mayor has to say is, 'You are released from the non-disclosure agreement,'" Biden said, adding, "This is about transparency." 

Asked for a final comment, Bloomberg said, "We are not going to end these agreements because they were made consensually, and they have every right to expect that they will stay private." That response earned him another round of boos.

Changing norms in the face of #MeToo.

Those boos should have told Bloomberg he is on the wrong side of history. American companies -- maybe including yours -- have a longstanding tradition of stringent damage control when faced with harassment or discrimination complaints. These tactics include non-disclosure agreements and also employment contracts that force those with complaints to use binding arbitration, rather than civil or criminal court, to seek redress. These contracts allow the company to preserve its brand and reputation. But another way to look at it is that they allow companies to conceal the severity of a toxic workplace, and to protect the jobs of highly valued executives who repeatedly engage in inappropriate behavior.

But though such contracts are widespread throughout American companies, they're disappearing at some of the most high-profile tech companies in the land. Faced with the #MeToo movement and a 17,000-employee walkout, Google ended its forced arbitration policy last year. Facebook, Airbnb, and eBay have all ended forced arbitration policies as well.

The 78-year-old Bloomberg looked very much old-school as he stood onstage and tried to defend preserving these non-disclosure agreements to save the victims' privacy, when in all likelihood those victims were either paid for their signatures or coerced into giving them. It did not look good for his future ambitions as president. Whatever your future ambitions are, don't make the same mistake.

Here's the whole exchange.