FRED HIATT: Democrats, don’t celebrate Trump’s nomination. Fear it. “When I hear smart people explaining why Trump cannot win, all I can think is: Aren’t you the ones who told us that he couldn’t top 30 percent, and then 40 percent, and then 50 percent in the Republican primaries? Weren’t you confident that he was finished after he called Mexicans rapists, and insulted prisoners of war, and dished out a menstruation insult? Did you predict his nomination? If not, we don’t want to hear your certainty about his November defeat.”