The WHO is an agency of the United Nations tasked with coordinating responses to public health emergencies between nations. The United States is a founding member of the organization, which was set up in 1948 in the wake of World War II.

Ooh, that’s a big one,” Donald Trump said Monday as he signed an executive order – one of dozens during his first hours as president – to withdraw the United States from the World Health Organization.

The U.S. has traditionally been the most generous benefactor of the WHO. A Trump executive order to cut ties with the WHO could pose a threat to global public health.