New York Times publisher A.G. Sulzberger wrote an op-ed in The Wall Street Journal on Wednesday warning that President Trump's recent “treason” accusation against the paper marks an escalation in his attacks on the media and “should concern every patriotic American.” “There is no more serious charge a commander in chief can make against an independent news organization. Which presents a troubling question: What would it look like for Mr. Trump to escalate his attacks on the press further?” Sulzberger wrote. “Having already reached for the most incendiary language available, what is left but putting his threats into action?” Sulzberger argued that the administration’s attack on the free press has already started—citing an increase of leak investigations, the attempt to block the AT&T-Time Warner (owner of CNN) merger, and the use of the Espionage Act against Wikileaks founder Julian Assange.

“Mr. Trump’s campaign against journalists should concern every patriotic American,” he wrote. “A free, fair and independent press is essential to our country’s strength and vitality and to every freedom that makes it great.” The op-ed came in response to Trump tweeting over the weekend to claim the Times committed a “virtual act of Treason” by publishing a story about his administration’s cyber offensive against Russia.