If you’ve followed the polls this week, you know exactly what this is about. Gary Johnson and, to a lesser extent, Jill Stein are peeling off huge numbers of voters aged 18-29, which is turning a tight two-way race into a Trump lead in the four-way. She could afford to give away young voters back when she was leading by six points. She can’t afford it anymore. So it’s all hands on deck for Democrats, with Bernie Sanders, Elizabeth Warren, and Michelle Obama set to campaign for Clinton soon to put the fear of God into millennials. And now Hillary...