TURKISH PRESIDENT Recep Tayyip Erdogan is plunging ever deeper into the destruction of what remains of a free press. His behavior resembles that of a despot rather than a leader of a NATO democracy. On Friday, with a court order, the state moved to seize Zaman, Turkey’s most widely circulated newspaper, and its sister publication, Today’s Zaman, ousting the management and editorial board and installing three court-ordered administrators. A similar process has been used before in Turkey to effectively take over and close down media outlets. “We are going through the darkest and gloomiest days,” Today’s Zaman told readers in an editorial protest. In a defiant last edition before the takeover, Zaman said in a huge Page 1 headline, “The Constitution is suspended.”

Just recently, Mr. Erdogan moved against two prominent editors, Can Dundar and Erdem Gul, from the newspaper Cumhuriyet, accusing them of treason for publishing information about weapons transfers by the Turkish secret service to fighters in Syria. The charges were trumped up to intimidate and harass all independent journalists in Turkey. Both editors were jailed in November, but the Turkish Constitutional Court ordered them released from detention Feb. 25, pending the start of their trial March 25.

Now Mr. Erdogan has turned against Zaman and Today’s Zaman, closely affiliated with Fethullah Gulen, a Muslim cleric who lives in self-imposed exile in Pennsylvania. Once an ally of Mr. Erdogan, he has become a leading target of the president’s wrath. Mr. Gulen’s Hizmet movement has millions of followers in Turkey, but the president has depicted it as some kind of shadowy conspiracy bent on ousting him from office, and adherents have been prosecuted based on the nation’s antiterrorism laws. By seizing Zaman and Today’s Zaman, Mr. Erdogan is reaching for the movement’s throat. Barely two days after ousting the editors and management, Zaman began printing pro-government articles.

It is only the latest of his repressive moves: Journalists critical of the government have been forced out of their jobs; social media have been blocked; academics have been targeted for speaking out against Turkey’s military campaign against Kurdish separatists; and Mr. Erdogan is seeking to rewrite the constitution to expand the president’s powers. Asli Aydintasbas, a prominent journalist, told the New York Times, “Turkey is galloping towards an authoritarian regime full speed ahead.”

That gallop should worry the United States. Turkey is an ally and hosts NATO tactical nuclear weapons. It is sliding into the abyss of one-man rule. Of course, Turkey is struggling with urgent problems, including an influx of nearly 2 million refugees from Syria. Mr. Erdogan may calculate that Europe and the United States will not dare object to his crackdown as long as they need his help to keep refugees from flooding Europe. He should be proved wrong. The time to speak out is now, before freedoms have disappeared and Turkey is ruled by a single strongman.