Experts have also cautioned that withdrawing from the organization could weaken the world’s defenses against new outbreaks capable of triggering pandemics.

Here’s a look at what Trump’s decision means:

What happened?

During the first Oval Office appearance of his second term, Trump signed an executive order detailing how the withdrawal process might begin.

“Ooh,” Trump exclaimed as he was handed the action to sign. “That’s a big one!”

His move calls for pausing the future transfer of U.S. government funds to the organization, recalling and reassigning federal personnel and contractors working with WHO and calls on officials to “identify credible and transparent United States and international partners to assume necessary activities previously undertaken by” WHO.

This isn’t the first time Trump has tried to sever ties with WHO. In July 2020, several months after WHO declared COVID-19 to be a pandemic and as cases surged globally, Trump’s administration officially notified U.N. Secretary-General Antonio Guterres that the U.S. was planning to pull out of WHO, suspending funding to the agency.

President Joe Biden reversed Trump’s decision on his first day in office in January 2021 — only to have Trump essentially revive it on his first day back at the White House.

What is WHO and does this really matter?

It is the U.N.’s specialized health agency and is mandated to coordinate the world’s response to global health threats, including outbreaks of mpox, Ebola and polio. It also provides technical assistance to poorer countries, helps distribute scarce vaccines, supplies and treatments and sets guidelines for hundreds of health conditions, including mental health and cancer.

“A U.S. withdrawal from WHO would make the world far less healthy and safe,” said Lawrence Gostin, director of the WHO Collaborating Center on Global Health Law at Georgetown University. He said in an email that losing American resources would devastate WHO’s global surveillance and epidemic response efforts.

New Zealand’s former prime minister Helen Clark said it wasn’t in American interests to pull out of the agency now, particularly given the “ghastly proposition” that the increased spread of bird flu there might turn into a pandemic.

She described Trump as “a disruptor” and said the loss of American funding to WHO would cause “quite a substantial dent” to the agency.

Can Trump really withdraw the US from WHO?

Yes, as long as he gets the approval of Congress and the U.S. meets its financial obligations to WHO for the current fiscal year. The U.S. joined WHO via a 1948 joint resolution passed by both chambers of Congress, which has subsequently been supported by all administrations. The resolution requires the U.S. to provide a one-year notice period should it decide to leave WHO.

What does this mean for WHO?

It’s extremely bad. The U.S. has historically been among WHO’s biggest donors, providing the U.N. health agency not only with hundreds of millions of dollars, but also hundreds of staffers with specialized public health expertise.

In the last decade, the U.S. has given WHO about $160 million to $815 million every year. WHO’s yearly budget is about $2 billion to $3 billion. Losing U.S. funding could cripple numerous global health initiatives, including the effort to eradicate polio, maternal and child health programs, and research to identify new viral threats.

American agencies that work with WHO would also suffer, including the CDC. Leaving WHO would exclude the U.S. from WHO-coordinated initiatives, like determining the yearly composition of flu vaccines and quick access to genetic databases run by WHO, which could stall attempts to produce immunizations and medicines.

Why is Trump withdrawing the US from WHO?

At a September campaign rally, Trump said he would “take on the corruption” at WHO and other public health institutions that he said were “dominated” by corporate power and China.

His executive order Monday said the U.S. was withdrawing from WHO “due to the organization’s mishandling of the COVID-19 pandemic that arose out of Wuhan, China and other global health crises” and cited the agency’s “failure to adopt urgently needed reforms” and its “inability to demonstrate independence from the inappropriate political influence of WHO member states.”

WHO made several costly mistakes during the pandemic, including advising people against wearing masks and asserting that COVID-19 was not airborne. The agency only officially acknowledged last year that the virus is indeed spread in the air.

During its efforts to stop COVID-19, WHO also dealt with the biggest sexual abuse scandal i n its history, when media reports revealed that dozens of Congolese women had been sexually harassed or assaulted by health responders working to contain Ebola. The AP found senior managers were informed of some instances of sexual abuse when they occurred in 2019 but did little to stop them or punish perpetrators.

What has WHO said?

In a statement Tuesday, WHO said it “regrets” Trump’s announcement.

“We hope the United States will reconsider and we look forward to engaging in constructive dialogue to maintain the partnership between the USA and WHO,” the organization said.

“For over seven decades, WHO and the USA have saved countless lives and protected Americans and all people from health threats. Together, we ended smallpox, and together we have brought polio to the brink of eradication,” WHO said.

At a Geneva news briefing on Tuesday, WHO spokesperson Tarik Jasarevic said the U.S. contributed 18% of WHO’s budget in 2023, making it the single biggest donor that year. He declined to say what the U.S. withdrawal might mean for WHO.