The title of this piece pays homage to Karl Popper’s great work of political philosophy, The Open Society and Its Enemies. Popper wrote the book during the Second World War in an attempt to explain — and refute — the totalitarian ideologies that had delivered Europe into the hands of murderous dictators like Stalin and Hitler.

In Volume I, Popper traces totalitarianism’s roots back to Plato’s dictum, “The wise shall lead and rule, and the ignorant shall follow.” Despite its obvious appeal to intellectuals who see themselves as potential philosopher kings, Popper argues that this principle of governance should be rejected, not just because it is mistaken, but because it reflects a misguided approach to political inquiry. The fundamental political question, he suggests, is not, “Who should rule?” It is, “How can we so organize political institutions that bad or incompetent rulers can be prevented from doing too much damage?”

While Popper’s suggestion was regarded as heretical by many of his contemporaries, it wasn’t actually new. The Constitutional Convention delegates who assembled in Philadelphia in 1787 understood that preventing bad or incompetent rulers from doing too much damage was an important part of their task. That’s why the Constitution of the United States — which they signed 232 years ago today — included many features that constrained the power of government. The members of the first U.S. Congress and the various state legislatures understood it, too. That’s why the Constitution was amended to include additional constraints in the form of the Bill of Rights.

In the years following ratification, other countries began to imitate America’s approach to institutional design, in many cases by adopting written constitutions of their own. And as these liberal institutions took root, they set the stage for an unprecedented period of global peace and prosperity.

Sadly, instead of being thankful for these happy developments, many intellectual and political leaders turned against the ideal of limited, constitutional government and transferred their allegiance to ideologies like communism and fascism that offered a more exciting vision of the future. Popular support for these ideologies blossomed in the chaos and disillusionment that followed the First World War, and — in one European country after another — totalitarian dictators took control.

The same thing very nearly happened here. Beginning in the 1890s, self-styled American “progressives” also turned against the ideal of limited, constitutional government. They advocated an alternative system based on centralized control by a technocratic elite, and support for this new approach spread rapidly. By the election of 1912, both Teddy Roosevelt and Woodrow Wilson ran on explicitly progressive platforms. By 1920, the progressives had achieved one of their primary policy goals — the prohibition of alcohol. By 1928, a decision by the most progressive justice on the Supreme Court, Oliver Wendell Holmes, had cleared the way for another goal— racial purification through involuntary sterilization.

In order to achieve results like these, progressives had to overcome numerous constitutional impediments, and, because those impediments remained the law of the land, the courts struck down many of the progressives’ other attempts to regulate Americans’ lives. Nevertheless, the progressives never attempted formally to overthrow the Constitution. Instead, they promoted a progressive theory of law designed to undermine the Constitution’s power.

The theory held that laws in general, and the Constitution in particular, should be regarded as “living” documents, the meaning of which could and should be manipulated to suit changing conditions and changing ideas of what is desirable. It also held that, rather than trying to enforce the checks and balances specified by the Constitution, courts should simply presume the constitutionality of any legislation that was not clearly irrational.

While the Supreme Court resisted this theory for a long time, it capitulated in the 1930s under intense pressure from President Roosevelt, and progressive legal theory became legal doctrine. While not ideal, this rough compromise between progressives and constitutionalists was vastly superior to what happened in Europe. Preserving the form of the Constitution meant that the courts could go on protecting constitutional rights as long as those rights didn’t run afoul of progressives’ wishes. It also left open the possibility that the Constitution might eventually be revived, which is exactly what has happened.

The appointment of two committed constitutionalists, Antonin Scalia and Clarence Thomas, changed the balance of power on the court. Between them they revived the constitutional ideals of limited government and legally enforceable rights and made them respectable among legal scholars and judicial decision-makers. Sadly, Scalia died in 2016, but the recent appointment of two more constitutionalists, Neil Gorsuchand Brett Kavanaugh, means the Constitution is probably safer today than at any time in the past 100 years.

None of this would have surprised Karl Popper. In The Open Society and Its Enemies, he emphasized the need for institutional limits on political power, but he also acknowledged that the mere creation of such institutions is not enough. “Institutions,” he said, “are like fortresses. They must be well designed and well manned.” Fortunately for us, the institutions that make up our constitutional order were both. As a result, we were spared the worst of the devastation that totalitarianism visited upon the world in the 20th century, and we can look forward to the possibility of constitutional revival in the 21st.

We cannot afford to be complacent, however. Today’s would-be philosopher kings are just as hungry for power as their 20th-century predecessors, and they are just as willing to destroy the institutions of constitutional government in order to get it. To prevent that, we must make sure those institutions continue to be well manned in years to come.

Jon Guze is director of legal studies for the John Locke Foundation.