This measure, which China and Russia voted for, didn’t make Ebola any less deadly. But it shook up world leaders and offered a vital show of solidarity with the governments and peoples of West Africa in a context in which having a sense that the crisis could be solved played a decisive role in giving Africans the hope they needed to change behaviors that were aiding the spread.

Despite Mr. Trump’s disdain for international organizations like the World Health Organization (the U.S. contribution to which he attempted to halve just two months ago) and despite Washington’s own bungled domestic response, we nonetheless must immediately begin to build a broad and determined global anti-Covid coalition. Such a coalition must create hubs for sharing scientific data on the virus, testing and vaccine efforts, taking advantage of the staggered movement of the disease and every country’s ability to learn from infection cycles that have peaked earlier.

It must regularize frequent high-level political contacts to enable speedy decision-making, and the procuring and distribution of resources beyond the home front. It must apply pressure on those countries failing to come clean on case numbers. And it must assemble a mechanism that gathers volunteers, funds and in-kind contributions from U.N. member states, businesses and philanthropists to provide tailored support for particular vulnerable communities. Neither the U.N. secretary general nor the director general of the W.H.O. has the convening power or the leverage to perform this role unless the United States gets behind the effort.

Third, while the day may come when China can build and lead an effective global coalition, that day is not here. Much has been made of the fact that China is sending protective equipment to Ireland, Italy, Serbia and other nations, while the Trump administration has been forced to plead with South Korea and Russia for donations. China clearly sees both an opportunity to clean up the reputational damage done by its early mishandling of the crisis and a chance to showcase its generosity and superpower status.

There is no question that by the time this crisis is over, China will end up the largest international donor of precious medical provisions, which will hopefully help save countless lives. But sending supplies is not the same as leading the world.

Whatever its rhetoric about building a “Health Silk Road,” China has never built a global crisis coalition, in any sphere. Although China has more foreign diplomatic posts than the United States, Chinese officials have little experience hustling governments or private actors for contributions, while U.S. diplomats have been doing this for decades. Also, Chinese diplomats will not urge, for example, Bangladesh to turn on the internet in its refugee camps to allow public education, or Egypt to stop suppressing information. The United States and China urgently have to do what neither does easily, which is to put the blame game and larger competition aside, identify their comparative strengths and join forces.

It may well be that Mr. Trump’s inability to recognize the extent to which U.S. security is tied to that of others makes him incapable of reversing course and building a global coalition. But given the pressure he feels to restart the economy and normal life, this should be the wake-up call he needs that walls won’t protect us. Unless the United States exerts leadership to prevent Covid-19 from raging out of control abroad, the crisis will not end at home.

Samantha Power (@SamanthaJPower) is a former United States permanent representative to the United Nations and the author, most recently, of “The Education of an Idealist: A Memoir.”

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