It’s rare for public opinion on social issues to change sharply and swiftly. About half of American adults believe police violence against the public is a “very” or “extremely” serious problem, according to a poll conducted earlier this month by The Associated Press-NORC Center for Public Affairs Research. Only about a third said the same as recently as last September, as well as in July 2015, just a few months after Freddie Gray, a Black man, died in police custody in Baltimore.