Charles McMillan, a witness to George Floyd’s murder, speaks at the site where Floyd was killed on May 25, 2020, in Minneapolis.Stephen Maturen/Getty Images Thomas D. Beamish, University of California, Davis Tragedy seldom unifies Americans today. Every year, horrific crises induce tremendous suffering. Most are privately tragic, affecting only those directly harmed and their immediate relations. A small number, though, become politically notorious and, therefore, publicly tragic. Natural disasters, school shootings, terrorist attacks and economic crises can become public tragedies. Sexual ass…