President Obama took time during a press conference today to assail the spread of fake news online, particularly the way it travels on Facebook. “In an age where there’s so much active misinformation and it’s packaged very well and it looks the same when you see it on a Facebook page or you turn on your television,” he said, “if everything seems to be the same and no distinctions are made, then we won’t know what to protect.”

Obama’s remarks come at a time when Facebook has been subject to withering criticism for allowing fake stories and hoaxes to spread to millions of users at a critical time. A BuzzFeed analysis this week found that top-performing fake stories performed better on Facebook during the run-up to this month’s presidential election than accurate stories shared by traditional media sites.

Obama made his remarks during a joint press conference in Germany with its chancellor, Angela Merkel, during a valedictory tour of Europe. He appears to have been thinking about Facebook’s fake-news problem for a while: a profile about his final days as president in The New Yorker today said he had talked “obsessively” about a BuzzFeed report on how Macedonian teens were spamming Facebook with fake Trump news for fun and profit.

“Everything is true and nothing is true.”

In such a world, “everything is true and nothing is true,” Obama told New Yorker editor David Remnick. “An explanation of climate change from a Nobel Prize-winning physicist looks exactly the same on your Facebook page as the denial of climate change by somebody on the Koch brothers’ payroll. And the capacity to disseminate misinformation, wild conspiracy theories, to paint the opposition in wildly negative light without any rebuttal — that has accelerated in ways that much more sharply polarize the electorate and make it very difficult to have a common conversation.”

For its part, Facebook (along with Google) moved this week to ban sites that post fake news from using its advertising network to make money. But CEO Mark Zuckerberg has resisted the idea that the company played a role in influencing the outcome of the US election, calling the idea “crazy.” Still, he said the company would do more to combat the spread of fake news — while saying Facebook would resist becoming an “arbiter of truth.”

You can watch Obama’s full press conference below. His comments about fake news begin 48 minutes in.