President Trump’s decision this week to walk away from the Iran deal is significant for many reasons — but perhaps most importantly, it is yet another sign that America has lost faith in, and is no longer leading, the global system it imagined and built after World War II.

The global system that exists today — while imperfect— is among America’s most consequential achievements. After the carnage of two world wars, our nation’s leaders made what was a truly historic choice for humankind: We chose to construct a new world that had as its foundation liberty and dignity for all the world’s peoples, and self-determination for all the world’s nations. This new system, best exemplified by the United Nations (which was located and remains here in the United States), was an extension of the vision of our Founding Fathers, who fought a revolution and designed a governing system intent on ensuring that human liberty would prevail over tyranny, which we know today as authoritarianism.

It is hard both to overstate what a noble decision this was by our nation, and how successful it has been in leading mankind to a far better place. The postwar era has seen the end of colonial empires, the establishment of dozens of new countries and, as hoped, no great global conflagration on the scale of the wars of the early 20th century. The number of people on our planet has increased threefold, and extreme poverty has plummeted. We continue to witness astonishing advances in science, medicine and technology all across the world. The sheer number of people in every society who have the education levels, health and opportunity to contribute to their community has never been greater in all of human history. And the internet, while still young and finding its way, is spreading knowledge and connecting us all in ways unimaginable to previous generations.

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While our president has argued this global system has not been good for America, the facts are not on his side.

While our president has argued that this global system has not been good for America, the facts are not on his side. Many years into this post-WWII order, America remains the indispensable nation, with the most dynamic and powerful economy, the most feared and capable military and unrivaled soft and cultural power. Our inventions rest in the pockets and sit on the desktops of most of the people in the world. English is the world’s unofficial language, the dollar the world’s currency, American-style democracy still the aspiration for many of the world’s peoples, and many of the institutions constructed to guide the development of this new global order (including the U.N., the International Monetary Fund, the World Bank and the Organization of American States) remain in the United States. There has never been a society, in all of human history, as powerful as America is in the world today.

Our stock market is at all-time high, unemployment is reaching postwar lows, incomes have been rising at a rapid rate for several years and we came out of the Great Recession faster and more effectively than many other advanced economies. Crime rates are half of what they were a generation ago and more Americans have health insurance today than at any other time in the modern era. After years of struggle, cities across the nation have made remarkable comebacks, and many other societal indicators — teenage pregnancy, high school graduation and college attendance rates — are better than they’ve ever been. In the Obama era, we also made great advances in expanding the circle of opportunity to more and more Americans regardless of their immigration status, race, sexual orientation or gender.

Our nation and our world are not without challenges and problems, of course, but few presidents in American history have inherited a world or a nation in which more was going right than Donald Trump.

That is why the intensity of his desire to undo what was given to him remains so hard to understand.

But undo what he has been given with great intensity is exactly what he is doing. He walked away from the Trans-Pacific Partnership, a new Asian-orientated trade initiative meticulously negotiated with many of our most important allies that would not only have extended to the global trading system to more nations, but also modernized it to account for changes the internet has brought. He walked away from the Paris climate accord, making America the only nation in the world not a signatory to this historic initiative. He has bashed NAFTA and insulted Mexico and Canada, our close neighbors and America’s two largest export markets. He skipped the recent Summit of the Americas, an annual meeting established by the United States to foster more regional cooperation. He cheered Brexit, and appears at best ambivalent about the European project. He has questioned the integrity of NATO’s mission and repeatedly appeased (and even aided) Vladimir Putin’s efforts to undermine the West — most egregiously, by refusing to create a unified response to Russia’s new information warfare efforts, which remain active here in North America and Europe. And he has started imposing unilateral tariffs on our most important trading partners, a step that could literally begin to unwind the entire global trading system.

As durable and powerful and successful as the American-led post-WWII order has been, a sustained attack on it from its putative leader could eventually — and even rapidly — bring it down.

In a very short time Trump has turned the American presidency from the leader of the post-WWII order into its leading troll. His decision to walk from the Iran deal this week, a deal negotiated over many years with our closest allies, on a critical post-WWII order achievement — nuclear non-proliferation — was another powerful sign of Trump’s arrogant disdain for well-intentioned efforts by the nations of the world to prevent a return of the savagery of previous eras.

What remains most remarkable about Trump’s reckless approach to the world is that it has generated almost no debate here at home. We are at the point now in the Trump presidency in which responsible leaders of both parties have a deep and clear obligation to foster a sustained debate about the path Trump has chosen. As durable and powerful and successful as the American-led post-WWII order has been, a sustained attack on it from its putative leader could eventually — and even rapidly — bring it down. And if our leaders cannot find it within themselves to debate that, then perhaps America no longer deserves the global leadership role it so richly earned for so long.

Simon Rosenberg is the President of NDN, a center-left think tank in Washington. He has worked on issues involving globalization and the post-WWII order for over 25 years.