This month, federalism is getting a workout in a context as old as the nation itself. COVID-19 may be novel, but epidemics have been unwelcome visitors to American states and cities since the start. And under the Tenth Amendment of the U.S. Constitution, the Founders reserved public health emergency powers to the states.

When the coronavirus pandemic emerged, governors knew what they needed to do. But there was not enough trained personnel, equipment, test kits or cash on hand to do it. In the last two weeks we’ve watched them dust off their emergency public health response notebooks and assess the authorities that they have.