CAMBRIDGE – Since US President Donald Trump entered the political scene as a presidential candidate over a decade ago, observers have been scrambling to find some explanation for his bizarre words and deeds. Whenever we think we have exhausted the search, he says or does something even crazier, and the hunt begins again.

 

The first conclusion, popular during Trump’s first presidency, was that his assertions were never meant to be taken literally. But as he has followed through on a growing number of threats, from seeking revenge against political opponents to attacking Venezuela and kidnapping its president, this explanation has lost favor.

 

Another interpretation, advanced mostly by Trump’s supporters, focuses on his “America First” mantra: everything Trump does, however unexpected, is guided by America’s interests. But this claim is easy to dismiss. Regardless of what Trump believes, the United States has always acted in its own interests: while the open, liberal, rules-based order that the US has led since World War II was broadly good for the world, it benefited the US most of all.

 

Despite significant flaws, the post-WWII order delivered an unprecedented 80 years of relative peace and prosperity. This enabled the US to become an economic and geopolitical superpower, including by facilitating the US dollar’s rise as the premier international currency. If the system collapses, the US will be among the biggest losers.

 

In this sense, Trump is actively working against America’s interests. After all, unlike smaller countries, the US cannot free-ride on the international order. It must participate actively in maintaining and strengthening it by supporting free trade, preventing rogue actors from changing national borders by force, and contributing to shared solutions to global challenges like climate change and pandemics. Otherwise, the system may not survive – at least not in a form that serves the US. Europe is probably too disunited to fill the leadership vacuum left by the US, and China, should it step up, will not uphold America’s privileges.

 

In the same vein, some have argued that Trump’s actions reflect the frustrations and aspirations of the American workers who feel “left behind” by globalization, technological progress, and social change. But, far from helping this group, Trump’s policies tend to worsen their economic plight.

 

A good example is the ongoing Republican campaign to reverse former President Barack Obama’s signature legislative accomplishment, the Affordable Care Act, which dramatically expanded access to health care, not least for voters who would go on to form Trump’s base. Either Trump’s supporters do not see how the ACA benefits them – perhaps convinced by his efforts to paint it as a disaster – or they consider the ideological and cultural values Trump purports to represent to be more important. In any case, helping working Americans is clearly not Trump’s guiding principle.

 

The fourth popular explanation for Trump’s actions reflects his background in business. This is a “transactional” leader committed to negotiating deals that will bring narrow short-term benefits, even if it means undermining America’s credibility and long-term prospects. But most of his supposed victories have brought no discernable benefits at all for the US.

 

The argument that Trump’s deals are really about lining his own pockets, and those of family members and allies, is more compelling. But even seen through this lens, his behavior remains largely – and increasingly – incoherent. In fact, Trump increasingly evokes the memory of Caligula, the third emperor of Rome.

 

Though Caligula appeared reasonably rational when his reign began in AD 37, he seemed to descend into madness rapidly. He had sex with his three sisters, among many others. He built opulent villas and hosted lavish parties, thereby bankrupting Rome. He reversed all the actions of his predecessor Tiberius, while continuing to blame him for anything that went wrong. He declared war on the English Channel.

 

Caligula also grafted busts of his own head onto statues of gods, and demanded that people worship him as one. During a gladiatorial spectacle, he had a whole section of the audience thrown into the arena to be attacked by the lions. He humiliated senators by making them kiss his feet or run ahead of his chariot for miles. He tried to make his horse a consul.

 

The parallels with Trump are legion. The US president has a long history of sexual misconduct, and has repeatedly expressed interest in having sex with his daughter, Ivanka. As ordinary Americans struggle to make ends meet, he hosts extravagant parties at his Mar-a-Lago resort. He has added gold embellishments to the Oval Office and razed the White House’s historic East Wing to build a massive ballroom. And he blames his predecessor, Joe Biden, for America’s every woe.

 

Trump has built monuments to himself, affixed his name to memorials to others, and compared himself to God. He has sent armed forces to terrorize American cities. He makes Cabinet officials, CEOs, and foreign leaders pay obeisance to him, and attacks anyone deemed “disloyal.” He has debased Congress.

 

Trump has also insulted, alienated, and bullied America’s closest allies. In a letter to Norway’s prime minister, he explicitly linked his threats to invade and annex Greenland (which he repeatedly confused with Iceland in a January 21 speech at the World Economic Forum in Davos) to the decision not to award him a Nobel Peace Prize. Meanwhile, he rambles incoherently about windmills, sharks, and the fictional cannibal Hannibal Lecter.

 

Observers have been largely reluctant to pass judgment on Trump’s mental health, partly because calling him “crazy” or “demented” can seem like a casual insult tossed at a public figure with whom one disagrees. Be that as it may, I now join those, including former supporters, who can no longer avoid the obvious conclusion: Trump is America’s Caligula.

 

Jeffrey Frankel, Professor of Capital Formation and Growth at Harvard University, served as a member of President Bill Clinton’s Council of Economic Advisers. He is a research associate at the US National Bureau of Economic Research.