This is a scary moment in America, and we need a leader who won’t exploit the chaos. Someone who can strike just the right tone – with humanity, and moral clarity– that trickles down to other leaders in both parties, reminding us of our values, our better selves. Joe Biden rose to the occasion. He expressed sincere empathy for Donald Trump and other victims of Saturday’s horrific attack, including a father killed while protecting his family from bullets. He called on all Americans to “lower the temperature in our politics,” and to reject violence in any form. He did his part, dialed it down, a…