After a brief truce last month, the war between the U.S. president and the media is again in full flame. But this week the stakes changed. Trump issued a tweet suggesting that some news networks should have their licences challenged or revoked. His critics pounced, suggesting that he had violated the First Amendment, for which he could be impeached. Press-freedom activists opined that Trump's tweet alone was actionable. Rebecca Baker, president of the Society for Professional Journalists, threw cold water on the idea. "Right now it's just his words," she said, "no executive orders, no bills introduced to Congress, just hot air." But the cat is among the pigeons. Goading Trump now has strategic value.