The Stafford Act, a 1988 law that amended the 1974 Disaster Relief Act, authorizes the president to declare either a “major disaster” or an “emergency” for the purpose of providing assistance to state and local governments whose resources have been overwhelmed. In this case, the president declared an emergency, but he also announced that he considered the coronavirus to meet the law’s definition of a “major disaster,” and invited states’ governors to request that he issue major-disaster declarations.

The definition of major disaster is fairly limited: It is confined to natural catastrophes, fires, floods, and explosions. The definition of emergency is much broader—“any occasion or instance for which, in the determination of the President, Federal assistance is needed to supplement State and local efforts and capabilities to save lives and to protect property and public health and safety, or to lessen or avert the threat of a catastrophe”—but some types of assistance available under a major-disaster declaration are not available under an emergency declaration. For either type of declaration, the Federal Emergency Management Agency is the responsible agency, and the source of funding is the Disaster Relief Fund—which currently contains more than $40 billion.

Under a Stafford Act emergency declaration, the federal government can perform various activities to support state and local emergency assistance. It can coordinate disaster-relief efforts, provide technical and advisory help to state and local governments, provide grants to individuals and households for temporary housing and personal needs, and distribute medicine and food. Under a major-disaster declaration, the federal government can provide additional forms of assistance—most notably, direct relief to victims and communities affected by the disaster in the form of unemployment assistance, food coupons, legal services, grants to assist low-income migrant and seasonal farmworkers, emergency public transportation, and emergency communications.

Even though a pandemic could clearly meet the Stafford Act’s definition of an emergency, using the law for such a purpose is actually quite unusual. Rather, federal responses to such crises generally take place under the auspices of the Department of Health and Human Services, using authorities provided by a different law, the Public Health Services Act (PHSA). In fact, a president has declared a Stafford Act emergency to address an outbreak of disease on only one prior occasion: In 2000, President Bill Clinton issued Stafford Act declarations in response to requests from the governors of New York and New Jersey to address an outbreak of the West Nile virus. No president has ever declared a major disaster in response to a health epidemic.

The other law on which Trump’s Friday declarations relied, the 1976 National Emergencies Act (NEA), represents an entirely different and far more dangerous model of emergency powers. The law itself confers no emergency authorities, but rather authorizes the president to invoke special powers contained in more than 100 other provisions of law, by virtue of declaring a “national emergency.” Unlike the Stafford Act, the NEA does not define what constitutes a qualifying emergency; that decision is left to the president. In the declaration, the president must specify which powers he intends to invoke, and he must issue updates if he adds new powers to the list.