President Trump and first lady Melania Trump made a surprise visit to American troops in Iraq on Wednesday, marking the president’s first trip to a U.S. military combat zone.

Mr. Trump made a three-hour visit to the al-Asad Air Base in western Iraq, near the Syrian border. Upon arriving at a dining hall, the president received a standing ovation from the troops. He posed for selfies and signed several red “Make America Great Again” hats that service members had brought.

While...