Defense Secretary Mark T. Esper said Sunday that President Trump ordered a withdrawal of American forces from northern Syria, a decision that will effectively cede control of the area to the Syrian government and Russia, and could allow a resurgence of the Islamic State. Mr. Esper, appearing on both Fox News and CBS News, said that American troops, mostly Special Operations forces, would leave the northeastern part of the country in the face of Turkey’s incursion into the section of Syria controlled by Kurdish forces, a group of fighters trained and backed by the United States government. The bulk of...