IF A person is to be judged by his enemies, George Soros can feel proud. Autocrats across Eastern Europe, including his native Hungary, as well as those from China to Egypt and many in between, have expressed fear and loathing — and taken action against — the civil society organizations that Mr. Soros has generously supported for three decades. Dictators do not like Mr. Soros at all, so it is good news that he has now contributed $18 billion of his fortune to his Open Society Foundations.

The contributions, made in recent years but disclosed only this week, will make Open Society the second-largest philanthropic organization in the United States, behind the Bill and Melinda Gates Foundation. Mr. Soros has now created a philanthropic superpower for liberal democracy.

And none too soon. The past decade, in particular, has witnessed a rising tide of illiberalism across the globe. The Stanford University-Hoover Institution scholar Larry Diamond calls this the decade of democratic recession. From Presidents Xi Jinping of China and Vladimir Putin of Russia to Recep Tayyip Erdogan of Turkey, Abdel Fatah al-Sissi of Egypt, Hun Sen of Cambodia, Nicolás Maduro of Venezuela, Viktor Orban of Hungary and Ilham Aliyev of Azerbaijan, government leaders have been aggressively rolling back democracy and human rights. They have used traditional coercion such as imprisoning innocent people for dissent or for expressing views freely in news and social media. They also have subverted freedom by staging "elections" that are rigged; funding news media that are not independent; labeling civil society organizations as "foreign agents" or spies; blocking access to the Internet; and other insidious and innovative techniques.

Mr. Soros, who lived in Nazi-occupied Hungary as a boy, is at the forefront of pushing back against totalitarianism and authoritarianism, and his new commitment suggests that his foundations will sustain this mission for years to come. Mr. Soros was moved many years ago by the 1945 book by Karl Popper, "The Open Society and Its Enemies," written during the struggle against totalitarianism in World War II but holding lessons for today. Then as now, a healthy civil society — the connections of free citizens to one another through the press, informal associations, advocacy organizations and otherwise — is the bane of authoritarianism.

Alas, even the richest foundations cannot fill the gap left when governments fail to act. This is salient and urgent now as President Trump turns his back on decades of U.S. support for democracy and human rights. Nothing compares to the persuasive power and overarching influence of the United States as the exponent of freedom.

As former president George W. Bush said in an important address on Thursday, "For more than 70 years, the presidents of both parties believed that American security and prosperity were directly tied to the success of freedom in the world. And they knew that the success depended, in large part, on U.S. leadership." For all the positive works Mr. Soros envisions for his billions, it would be doubly good if the government of the United States were walking in tandem with him, and it is a tragedy that it is not.