A wave of police killings of young black men in 2014 prompted 24 states to quickly pass some type of law enforcement reform, but many declined to address the most glaring issue: police use of force. Six years later, only about a third of states have passed laws on the question. The issue is at the heart of nationwide protests set off by the May 25 death of George Floyd, a black man who died after a white police officer in Minneapolis pressed a knee into Floyd’s neck for several minutes while he pleaded for air.