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.

Experts have also cautioned that withdrawing from the organization could weaken the world’s defenses against dangerous new outbreaks.

One of President Trump’s first executive orders removes the U.S. from the global health organization, which experts say is “cataclysmic.”