That issue was and is police brutality.
And while I know that Whites, both male and female, are all too often victimized by unprofessional or brutal police acts, the most egregious instances of police misconduct are those faced by Black Americans and, specifically, African American men.
The paradigm and historical analogy that is closest to this problem of police use of illegal or excessive force, including deadly force, would be to recall the days when Black Americans were killed extra-legally by lynchings.
The major Senate and midterm elections should teach all Americans, especially Democrats, one thing about the nature of the 21st century American electorate: Democrats do not win without Black voter turnout.
Perhaps, the silence of the Democratic candidates on the issue of police brutality will be the same silence America will also hear on Election Day, 2020.