Members of the Chinese navy watch as the USS Blue Ridge, the U.S. 7th Fleet flagship, arrives in Shanghai on May 6 for a regularly scheduled port visit. (Associated Press)

HARDLY A day goes by without evidence that the liberal international order of the past seven decades is being eroded. China and Russia are attempting to fashion a world in their own illiberal image; Britain is debating a departure from the European Union; Austria’s front-running presidential contender espouses fear of migrants, trade and globalization; and far-right parties are thriving in Europe. The radical Islamic State group wields merciless violence on its own lands in Iraq and Syria and exports terrorism beyond. In the United States, presumptive Republican presidential nominee Donald Trump has attracted millions of voters by campaigning against some of the foundations of American leadership in the world such as the defense alliance with Japan and South Korea, while Democratic candidate Bernie Sanders has drawn millions more with the false promise of trade protectionism.

This poses an enormous trial for the next U.S. president. We say trial because no matter who takes the Oval Office, it will demand courage and difficult decisions to save the liberal international order. As a new report from the Center for a New American Security points out, this order is worth saving, and it is worth reminding ourselves why: It generated unprecedented global prosperity, lifting billions of people out of poverty; democratic government, once rare, spread to more than 100 nations; and for seven decades there has been no cataclysmic war among the great powers. No wonder U.S. engagement with the world enjoyed a bipartisan consensus.

These impressive accomplishments need a renewed boost from the United States and Europe, yet the public debate is running in the other direction. As authors of the report point out, many around the world are worried about an American retrenchment and yearn for more, not less, from the United States. They do not want to accede to the values of Presidents Vladimir Putin of Russia and Xi Jinping of China, who reject democracy, accountability and human dignity.

The new report, which is impressively bipartisan in its signatories and was co-chaired by a Reagan administration official, Robert Kagan (now a Post columnist), and a Clinton administration official, James P. Rubin, suggests strengthening all elements of U.S. power: diplomacy, economics, military — expensive, but “well within our means.” They rightly point out that the “adaptability, resilience, and innovation” of the U.S. economic system is a source of global strength and influence. The big question is not whether we can afford it but whether we have the willpower to use it. How? In Asia, the Trans-Pacific Partnership, the proposed free-trade agreement, must be approved. The United States must keep trying to integrate China into the rules and traditions of the liberal international order — a policy of eight presidential administrations — while also marshaling forces to confront China’s assertive and unilateral grab of territory in the South China Sea. Likewise, stabilizing Ukraine and saving it economically will be a vital bulwark against Russia’s violent subversion. More needs to be done, too, to protect the Baltic states. In the Middle East, the liquidation of the Islamic State and ending the Syrian war will demand time and treasure from the United States. Today’s morass is in part the consequence of a leadership vacuum.

America’s global leadership demands movement on all these fronts while resisting facile populist appeals to turn inward.