WASHINGTON — When John H. Durham was assigned by the Justice Department in 2019 to examine the origins of the investigation into the 2016 Trump campaign’s ties to Russia, President Donald J. Trump and his supporters expressed a belief that the inquiry would prove that a “ deep state” conspiracy including top Obama-era officials had worked to sabotage him. Now Mr. Durham appears to be winding down his three-year inquiry without anything close to the results Trump was seeking. The grand jury that Mr. Durham has recently used to hear evidence has expired, and while he could convene another, there...