NATO Secretary-General Jens Stoltenberg on Tuesday signaled opposition to President Trump’s plan to pull more U.S. troops out of Afghanistan and he cautioned that “leaving too soon” could lead to terrorist strikes against America and its allies. In a statement, Mr. Stoltenberg said all NATO allies are eager to leave Afghanistan after nearly 20 years of war, but he stressed that a withdrawal must only happen when “the time is right” on the ground. His comments come after reports that Mr. Trump will soon issue formal orders to cut the number of American forces in Afghanistan from 4,500 to about...