Mark Zuckerberg has done his best to get around the problems that his giant social network has created in the form of viral fake news and hoaxes, a problem that many believe may have played a key role in the election of Donald Trump. But he can’t evade the issue much longer.

One of the arguments that the Facebook CEO offered when the fake news discussion first began was that the small proportion of fake news stories couldn’t possibly have affected the outcome of the election. This was “crazy talk,” he said.

But as a number of people quickly pointed out, Facebook’s entire marketing and advertising business, which is worth billions of dollars a year, is predicated on the idea that having your message on the platform can reach and influence hundreds of millions of people. Zuckerberg can’t have it both ways.

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The risk for Facebook is that if it shows that it either isn’t willing to or can’t control the spread of fake news on its network, then it is sending the message that it isn’t willing to or can’t control any of the other activity that takes place there either.

On Friday, Zuckerberg wrote a long post explaining that Facebook is concerned about the problem and is planning to take a number of steps to control it, including getting the help of outside news agencies and third parties to verify news. He needs to step that process up and quickly, or the media isn’t the only institution in which people are going to lose trust.