As demonstrators flooded streets across America to decry the killing of George Floyd, public health experts watched in alarm — the close proximity of protesters and their failures in many cases to wear masks, along with the police using tear gas, could fuel new transmissions of the coronavirus. Many of the protests broke out in places where the virus is still circulating widely in the population. In fact, an Associated Press review found that demonstrations have taken place in every one of the 25 U.S. communities with the highest concentrations of new cases.