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 US contributes around a fifth of the budget for the World Health Organization – its withdrawal from the public health body will impede efforts to control the global spread of diseases and could pu

It’s an action many scientists fear could roll back decadeslong gains made in fighting infectious diseases like AIDS, malaria and tuberculosis.