The problems keep piling up for Facebook, and it’s unclear how long the internet giant will be able to brush them aside as it barrels toward acquiring its next billion users.

The world’s biggest social network has unwittingly allowed groups backed by the Russian government to target users with ads. That’s after it took months to acknowledge its outsized role in influencing the U.S. election by allowing the spread of fake news — though before news emerged that it let advertisers target messages to “Jew-haters.”

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“As a practical matter, it is extremely difficult for the U.S. government to regulate content on the internet that may have an effect on the U.S. election,” said Nathaniel Persily, a professor at Stanford Law School. “If a teenager in his mother’s basement in Moscow wants to put up a YouTube video, it’s not clear what the U.S. will be able to do about that.”

Difficult doesn’t mean impossible. Persily, for instance, thinks that Facebook could use its AI technology to flag election-related ads that don’t bear the disclosures required by existing law.