The shift came in the face of a Turkish invasion and President Trump’s decision to withdraw U.S. forces, leaving vulnerable the Kurds who had long been the ground troops in the American fight against the Islamic State.

Faced with a fast-unraveling situation, Mr. Trump’s policy toward the region continued to fishtail. A week after essentially greenlighting Turkey’s assault, he announced that he would sanction Turkey for what he called “destabilizing actions,” raising tariffs on steel and suspending negotiations on a $100 billion trade deal with Ankara.

On the ground: The American pullback effectively cedes control of the entire country to Mr. Assad and empowers his allies Iran and Russia. It also jeopardizes hard-won gains against ISIS; when forces moved in to the town of Ain Issa on Monday, about 500 ISIS sympathizers took advantage of the mayhem and escaped detention, local officials said.

Reaction: A Saudi ambassador called the U.S. withdrawal “a disaster for the region.” Foreign ministers from all 28 E.U. member states agreed to stop selling arms to Turkey, the first time the bloc had reached such a decision about a NATO ally.

A homemade bomb escalates Hong Kong protests

A homemade explosive was detonated on Sunday via mobile phone in the Mong Kok district amid violent protests. It was the first time such a device had been used in nearly five months of demonstrations, the police said on Monday.