The virus was first detected by doctors in Wuhan, China, at the end of December, and the organization’s experts evaluated it for weeks before declaring it a global emergency. After the W.H.O.’s emergency committee convened on Jan. 22 and Jan. 23, its director general, Tedros Adhanom Ghebreyesus, said, “Make no mistake: This is an emergency in China,” but had declined to label it a global health emergency.

The organization eventually did so in an advisory published on Jan. 30, but it did not recommend any restrictions on international travel or trade. The next day, Trump went ahead anyway with banning travel from China, which he now claims saved “thousands and thousands of lives,” but the move might have come too late and included spotty screening. On March 11, Trump extended travel restrictions to include Europe; the W.H.O. labeled the outbreak a pandemic the same day.

Trump was heaping praise on the organization as recently as late February, when he insisted that the virus was “under control” in the United States.

But he is not alone in now criticizing the speed of the W.H.O.’s response. A Change.org petition demanding Ghebreyesus’s resignation has been signed by over 900,000 people.

What Trump rarely acknowledges is that he often played down the virus’s threat, even after the organization labeled it an emergency, and for months, he resisted the advice of members of his own administration to more aggressively confront it.