Rachel Scott reports from Chicago where Donald Trump questioned Vice Pres. Kamala Harris' race during a forum with Black journalists; Mary Bruce has the latest details on the plea deal struck by federal prosecutors with 9/11 mastermind Khalid Shaikh Mohammad and two other defendants at Guantanamo; in Paris, James Longman reports on Team USA's lead in the Summer Games, and the triathlon that kicked off with a swim in the river Seine after the water was determined to be safe; and more on tonight's broadcast of World News Tonight with David Muir.