This article originally appeared at RealClearDefense on July 26, 2016. It was co-authored with Andrew Stravers, a PhD candidate in the Government Department at the University of Texas at Austin.

In a widely read interview, Donald Trump, the Republican nominee for president, questioned the fiscal wisdom of the NATO alliance. Because some alliance members “are extremely rich,” Trump argued that they should be paying the United States to defend them. “If we are not going to be reasonably reimbursed for the tremendous cost of protecting these massive nations of tremendous wealth,” he said, “I would tell those countries, ‘Congratulations, you will be defending yourself.’”

These comments are yet another example of Trump’s dangerous foreign policy ignorance.

The idea that rich allies should pay for their own defense is undeniably appealing to many Americans. However, what Trump is proposing amounts to an international protection racket, premised on at least two faulty assumptions about the costs and benefits of the alliance. Trump ignores the many contributions NATO members have made to American military missions, fundamentally misunderstands the value of the alliance to American foreign policy, and overlooks the potentially immense costs of jettisoning it.

Alliance membership is a two-way street. NATO’s Article 5 guarantee mandates that members respond if another member is attacked. Article 5 has only been invoked once, in the aftermath of the September 11th terrorist attacks, and America’s NATO allies stepped up. In 2011, NATO and the United States had a combined presence of about 135,000 military personnel in Afghanistan. Of that force, about 45,000 were personnel from allied militaries—up from 35,000 in 2009 (with 30,000 American personnel). Throughout the war in Afghanistan, NATO has contributed between 30-60 percent of the total force on the ground.

The NATO contribution to the fight against al Qaeda and the Taliban saved American taxpayers—the ones U.S. allies are supposedly leeching off—a great deal of money. The cost of basing one soldier in Afghanistan for a year is estimated at $850,0000. In just the three years from 2009 to 2011, the NATO presence in Afghanistan saved the United States approximately $90 billion in troop costs. The NATO contribution over the course of the whole Afghan campaign is thus far in excess of $100 billion.

NATO also provides tangible benefits in the form of bases and logistical infrastructure. Take Trump’s own “plan” to destroy ISIS by cutting off its oil supply. Without bases in NATO countries, that mission would rely on aircraft carriers and ground forces transported from the United States, which would dramatically increase their cost. Furthermore, NATO allies already pay the United States to maintain a military presence in their countries. In 2004, the most recent year with available data, Germany provided over $1.5 billion in both direct and indirect compensation for the American military presence. Italy likewise provided over $350 million, and Turkey, the United Kingdom, and Spain paid almost $500 million combined.

But NATO would be worth its cost even without the contributions of its non-U.S. member states. This is where Donald Trump’s second faulty assumption comes into play.

It may be apocryphal, but the statement attributed to Lord Hastings Ismay that the purpose of NATO was to keep “the Russians out, the Americans in, and the Germans down” succinctly encapsulates the value of the alliance. NATO has been an important source of stability in international relations for seven decades precisely because it alleviates the need for rich countries to build military forces of their own.

Military competition between the great powers of Europe had been a source of instability and war for centuries, culminating in the two great global conflagrations of the twentieth century. The American military presence in Europe after World War II reduced the pressure on historical rivals, such as France and Germany, to begin a new round of military competition, reducing the chances of renewed tensions and another war. And the American commitment to NATO lowered the pressure on West Germany to build its own nuclear arsenal during the Cold War, reducing the chances of war with the Soviet Union.

With the Soviet Union gone, the benefits of reduced security competition in Europe may seem too intangible to be meaningful. But if Trump had his way and jettisoned the alliance because its members do not “pay their bills,” the costs would be far higher than what American taxpayers contribute to the alliance today. Even if the U.S. military no longer had a presence in Europe, it would likely wish to maintain standing forces sufficient for a potential war in Europe. The economic conditions after the Great Depression that allowed for rapid mobilization in World War II—a surplus of idle labor and manufacturing capacity—do not exist today. A force of the needed size, the capacity to deploy it across the Atlantic Ocean, and the necessary infrastructure for all this would be monumentally expensive.

America does pay a great deal for its military contribution to NATO. However, contrary to what Trump thinks, the alliance produces benefits for American security and American taxpayers that are both tangible and intangible. As such, the Republican nominee’s delusional cost-benefit analysis suggests a strategy that will leave America without allies and taxpayers poorer.

Matthew Fay is a defense policy analyst at the Niskanen Center and a PhD student in the political science program at George Mason University’s School for Policy, Government, and International Affairs. Andrew Stravers is a PhD candidate in the Government Department at the University of Texas at Austin.