The founding fathers of the United States sought to avoid the perils of monarchy – especially absolute monarchy. So they came up with the idea of a president who in certain respects would be absolute, in order to get things done, yet not in others. He (or she) would be beholden to Congress for laws and finance, and subject to the Supreme Court in terms of interpreting the US constitution once it was written and agreed. There would be term limits and a new election every four years.

With a number of hiccups (and there have been many, mostly notably the Civil War), this system of government has done astonishingly well – for America. And not badly for the rest of the world, either. With the advent of the Second World War and the development of the atom bomb, the US was, in effect, compelled to become an empire in all but name. It therefore became important to abide by President Franklin D Roosevelt’s simultaneous development of a “new world order”, as he called it. Eight other nations have acquired nuclear weapons (the UK, Russia, China, France, Israel, India, Pakistan and North Korea). By virtue of its economy and naval and air force reach, however, the US has remained, for better or worse, the leader of the pack. It is the only one enjoying global respect for its humanitarian ideals and its willingness, if necessary, to fight with coalition partners and actively defend them where necessary (even, arguably, where unnecessary).

Why, then, is Donald Trump, the 45th US president, so anxious to dismantle this achievement? The president, to be sure, is answerable to those who elect him (or her). This has produced a strange situation. A media that gave the former reality TV personality and property developer carte blanche to rant, rave and entertain us during his 2016 election campaign has now largely – and venomously – turned against him. This has led the president to complain repeatedly of “fake news” and a conspiracy by and in the media to bring him down. “No politician in history,” he has tweeted, “and I say this with great surety, has been treated worse or more unfairly.”

Behind the shouting, however, there are deeper factors at play in America and beyond. As a historian-biographer who has studied the presidency since the US became an empire in all but name, let me briefly point to a few.

First, the empire. Trump did not create the American empire. He knows nothing of its creation, does not read history and would be happy to see it collapse under its own weight, as the British, French and Dutch empires have collapsed in his lifetime. Brexit appealed to him as a deliberate casting-off of the kind of responsibilities and ideals that he scorns. In pulling the US out of international accords, trade agreements and so on, he is proudly carrying out an “Amerexit” – to “make America great again”, but as Great Little America.

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Whether this is wise or not is being debated in Washington, DC, and elsewhere. Isolationism is not new in American history, however. The US Senate refused to ratify the Treaty of Versailles, or approve American membership of the League of Nations in 1920. Backed by Congress, President Warren G Harding opted to put an end to lower tariffs and seek protectionism from foreign trade in the early 1920s; by the following decade, world trade had plummeted by almost two-thirds. Moreover, as European nations struggled with fascism and communism, the US electorate became profoundly insular and anti-immigrant, led by the America First movement.

It was only the Pearl Harbor attack and Hitler’s declaration of war against the US in December 1941 that changed the American consensus. That Roosevelt was able to move Congress and public opinion to embrace global responsibilities was a kind of miracle, especially for Jews and those countries the US liberated from Nazi or Japanese occupation. Such idealism was always a tough sale, but FDR’s efforts to ramp up the American war economy changed history.

As even Stalin acknowledged, the war against the Wehrmacht would have been lost without US mass production not only providing 12 per cent of Soviet war needs in resisting Hitler, but feeding the world economy and arming a huge American military in the air, at sea and on land. This enabled it to launch, against British fears and objections, the contested amphibious cross-Channel assault of D-Day – and, later, using the newly developed atomic weapons, to crush the Japanese empire, which continued to commit atrocity after atrocity in China and the Pacific.

The burgeoning of the US economy as the war was fought and won – as well as its commitment to free world trade – was then used to cover a multitude of American domestic and international sins, including the persistent cries of isolationists, anti-immigrants and trade protectionists.

In creating the United Nations in 1945 as a more effective international peace and security organisation than the League of Nations had been, Roosevelt established at least the framework for the diplomatic international discussion of global issues. For a variety of reasons – the Iron Curtain, the Chinese Civil War, on­going colonialism – the president’s concept of global security that would be guaranteed not by the US alone but by four major countries (America, Russia, China and the UK) did not come to fruition. Yet the principle behind his concept did survive – becoming a world order guaranteed by the US and the Soviet Union, backed by supportive lesser nations.

Despite hot moments, successive American presidents – Harry Truman, Dwight Eisenhower, John F Kennedy, Lyndon Johnson, Richard Nixon, Gerald Ford, Jimmy Carter, Ronald Reagan, George HW Bush and Bill Clinton – largely followed this “world order” script. However, with the economic ascent of post-Mao China, the fall of the USSR and the growing Shia-Sunni conflicts and internecine wars in the Middle East – often inflamed by impetuous American intervention – the notion of a stable world order began inevitably to wobble. It was only kept alive by a septuagenarian UN, an ageing Nato alliance and an elderly bipartisan American consensus, expressed in the abiding willingness of Congress and the majority of voters to take ultimate responsibility for world security. Not, however, by the 45th US commander-in-chief.

The American empire, in other words, was created by a single American commander-in-chief – arguably the greatest leader in American history – and is now being systematically dismantled by another American commander-in-chief.

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Scond, the economy, stupid. That mantra, written on blackboards in Governor Bill Clinton’s campaign headquarters when he was running for office in 1992, was chalked up to remind staffers of what the public most wanted to hear: namely his ideas on economic growth and higher pay.

Clinton’s attempt to provide health care for all proved a fiasco in 1993, but his economic measures and his tax increases on the rich defied Republican warnings of doom. The American economy boomed – the more so thanks to increased, not decreased, international trade and trade agreements. Behind the economic scenes, however, the world economy was bound to tilt towards other, more populous nations offering cheaper labour, especially in Asia – and it did. This would inevitably affect the world order.

President Clinton’s surpluses in the 1990s were quickly squandered by his successor, George W Bush, whose response to international Islamic terrorism was to attempt a late-imperial demonstration of unilateral military might, while perhaps hoping to get more oil. It didn’t work, all but bankrupting the exchequer in Washington, while its rising rival China expanded its economy without limitation.

With the continuing wars in Afghanistan and Iraq, the bills were due for payment. The US economy crumpled and, despite Barack Obama’s attempts to pull back from expensive dead-end foreign struggles, the underlying global economic shift towards Asia brought its predictable consequences in America. As incomes failed to rise in the same way as they had over the past seven decades and the great postwar US economic ascendancy approached its limit, suffering from unsustainable national debt, the centre would no longer hold.

Loud-mouthed Tea Partiers vowed to “kick out the bums” in Washington, DC – “bums” who were not providing the same well-paid jobs for relatively uneducated workers that such voters and their parents had enjoyed in America’s postwar heyday. White, male, formerly reliable working-class Democratic voters, in particular, found themselves humiliated by a professorial black president.

The blame game had thus started in earnest, with varying culprits burned in effigies: from Wall Street, on one hand, to federal regulators on the other. Moreover, with President Bush allowing the ten-year Clinton-era taxes on the rich to expire, and President Obama unable to get a Republican Congress to restore them, economic inequality in America bred not just contempt but hatred. Thanks to a Supreme Court decision allowing companies to back political parties and initiatives without financial limit, Obama’s Democratic successor-in-waiting was compelled to seek funds sufficient to face down a rising Republican campaign-finance juggernaut. As a consequence, Hillary Clinton was not even able to blame Wall Street, her backers, for the rising inequality in the nation.

“Stronger together” was the best mantra that Hillary Clinton’s campaign could come up with: she nobly allied herself with LGBT advocates and myriad underprivileged supporters. Yet it was not enough, at least under the American electoral college system, and the most unlikely of candidates – Trump, a maverick “businessman”, real estate mogul and TV personality who had appeared on a popular programme, The Apprentice, and bewitched fans and the press with his unpredictable behaviour, policy stands and refusal to make public his tax returns – ended up in the White House.

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Neither candidate, however, had dared to tell the bitter truth: that America could not be made “great” again, because this was no longer 1945. Or 1955. Or 1965. Or the years that followed, up to the end of the 20th century. As Roosevelt warned in a message to Congress in January 1944, the year before he died, America needed a second bill of rights, lest economic inequality split the nation and, as it had in Europe in the 1930s, result in “the spirit of fascism”.

Roosevelt’s policy – “the foreign policy that we have been following, the policy that guided us at Moscow, Cairo and Tehran” – was based on the common-sense principle best expressed by Benjamin Franklin on

4 July 1776: “We must all hang together, or most assuredly we shall all hang separately.”

Somehow the world did “hang together”, more or less, after Roosevelt’s death. It is now under increasing strain, as a new cold war with Russia threatens, chaos consumes the Middle East and North Korea sabre-rattles in the East. With a diminishing American economic share of the world pie and its citizens fighting with each other to protect or increase their own share of the remaining domestic pie, the US is unlikely to remain a willing or even able guarantor of peace and trade abroad.

As Roosevelt noted, “Unless there is security here at home, there cannot be lasting peace in the world.” He saw domestic security as closely linked with the willingness of Congress to provide for the many, not for the few.

America, in other words, is hurtling today towards Second World status. It lacks a leader who possesses any idea of how to prepare the nation for the changing structure of the world; a world in which Americans will have to share their relative decline more equitably at home, or face ever-worsening social and political fragmentation and conflict and diminishing authority abroad.

Blithely indifferent to this, the president resembles, in the view of many historians, the emperor Nero, fiddling while Rome burns. He lives in a Trump family cocoon, contenting himself with scoring points against his enemies on Twitter: “fake” Americans, since anyone who does not admire the Dear Leader is a fake American.

The realistic idealism that Roosevelt once inspired – and that subsequent American presidents carried like a baton in a relay race towards the future – has vanished from both of the main political parties. In consequence, the US may well revert to the Dust Bowl from which Roosevelt once rescued it.

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This leaves, third, the matter of the president’s personality – the purview of the biographer, or, in the current case, psycho-biographer. Many psychiatrists have pointed, in private, to the similarities between Donald Trump and Richard Nixon, despite their different childhoods. But they are permitted to say nothing. Why? Because the American Psychiatric Association (APA), which has 37,000 members, issued what is in effect a gag order – the “Gold­water rule” – in 1973, a few years after Senator Barry Goldwater sued Fact magazine for diagnosing him as being unfit to be president and won. Thereafter, no APA psychiatrist has been allowed to publish an attempted diagnosis, or warning, of any public figure’s mental functioning, lest they bring opprobrium on the profession.

Given President’s Trump’s widely acknowledged unfitness to serve either as president or commander-in-chief, owing to his instability, this has been something of a millstone in American presidential politics. Observers have thus increasingly been turning to biographers, who have no gag rule. Though seldom trained in psychiatry, modern biographers spend years investigating the lives of their subjects, whether alive or dead. Among such subjects, Nixon is currently receiving the most attention in America, since the unpredictability of his character, his erratic behaviour, his contempt for ethical norms and his willingness to invite impeachment by Congress make him somewhat of a ringer for the current occupant of 1600 Pennsylvania Avenue.

I count myself among them. Recently opened records have verified what I and other historians have averred: that “Tricky Dicky” deliberately sabotaged, or “monkey-wrenched”, the Paris peace talks to end the Vietnam War during the presidential election campaign of 1968, hoping to close the deal himself if he, not Hubert Humphrey, was elected. Nixon was elected but found that he couldn’t close the deal, with consequences that proved fatal for tens of thousands of Vietnamese and Americans. He asked his secretary of state, Henry Kissinger, to portray him in negotiations with the North Vietnamese as a loose, atomic-armed cannon, in order to try to get the enemy to negotiate. It didn’t work.

Ironically, by the end of his presidency, Nixon became such a loose cannon that his staff, it is widely believed, removed the nuclear authorisation codes from the briefcase – the so-called nuclear football traditionally carried close to him by his military aide. In addition to holding secret slush funds, Nixon became obsessed with his critics, targeting individual protesters, opponents and even political scientists for burglary followed by character assassination – including the break-in at Daniel Ellsberg’s psychiatrist’s office to discredit Ellsberg as mentally deranged for leaking the “Pentagon Papers”. (The psychiatrist’s filing cabinet is now displayed at the National Museum of American History in Washington.) Not content with this, the president’s “plumbers” then broke into the offices of Nixon’s political opposition, the Democratic party, at the Watergate. This time, they were caught.

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As the secrets of the Trump campaign and his administration’s malfeasance concerning Russia slowly leak out, and a federally appointed attorney seeks to investigate “Russiagate”, the 45th president’s reactions replicate those of the 37th president, Nixon. These comprise a deeper and deeper determination to lie and threaten his way out, including firing the head of the FBI James Comey; threatening to remove the justice department’s special counsel investigating the matter, Robert Mueller; threatening to fire the attorney general, Jeff Sessions; and even suggesting that he would pardon all those involved – including, if necessary, himself. (Richard Nixon notoriously claimed to David Frost: “When the president does it, that means it is not illegal.”)

Will it work? It is arguable that the Watergate investigation tipped Nixon, who was already mentally unstable, into his ultimate mental collapse, leading to scenes that no playwright could invent, from asking Kissinger to kneel and pray with him by the White House elevator to telling the American public at a televised press conference that he had “never profited from public service”, had “earned every cent” and had “never obstructed justice” – all demonstrable lies – and finally that, contrary to all indications, he was “not a crook”.

Ring a bell? Only eight months into the Trump administration, there are signs that those gagged psychiatrists who had grave worries about the president’s “aberrant behaviour” were spot on – and that Donald Trump is nearing a similar breakdown. He has been circling his wagons and appointing more and more military personnel to defend him, both from his opponents and a White House staff rendered chaotic by

his inability to provide consistent presidential leadership. At times, the White House has seemed like a kindergarten without a teacher in charge: at war with its own Republican Party, Congress and anyone who does not believe in the demi-divinity of the Dear Leader.

The effect of all this on America’s status in the world is significant. Indeed, it is as if, at times, the rest of the world is trying to take the strain of a leaderless America and refusing quite to believe that this is

happening. But it is.

There is, fortunately, increasing resistance across the nation to Trump’s destructive agenda towards health care, the environment, energy, education, research and immigration policies – an agenda that Roosevelt described, in 1944, as that of men (mostly) with their heads “buried deep in the sand”. Thus far, the country has therefore avoided the route taken in Germany in 1933 (especially in terms of Gleichschaltung): namely a Trumpification of all political power in the US, including both houses of Congress and the Senate, as well as the Supreme Court.

The reality is that the political strains inherent in the winning Republican Party coalition – one that combines Tea Partiers, the religious right, the Grover Norquist anti-tax lobby, disaffected miners, super-rich outsiders such as the Koch brothers and white supremacists (the “basket of deplorables”, as Hillary Clinton called them), along with the largely right-leaning, wealthy “1 per cent” in America, who once labelled Roosevelt as a “traitor to his class” – were bound to make the various factions turn on each other in an America that is contracting, not expanding. And especially when it is “led” by a narcissist – a self-obsessed maverick who seems interested ultimately only in his own family’s fortunes.

The reckoning, however, will surely come, affecting the world as well as American voters. A new formulation of the “world order” will have to take place if nuclear war is to be avoided. President Trump may well be forced to resign under the 25th Amendment to the US constitution, on the grounds that he is “unable to discharge the powers and duties of his office”.

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That outcome will not, however, change the dynamics of the global economy and the inevitable decline of the American empire. Besides, by whom will the 45th president be succeeded? Richard Nixon’s place was taken, after the forced resignation of Spiro Agnew as vice-president, by Gerald Ford, who was perhaps the most underrated and kindest of all American Caesars since the Second World War.

Donald Trump’s place in the White House, by contrast, would be taken by a strange, Tea Party-aligned, right-wing, anti-federal government, anti-immigrant amnesty, anti-abortion, anti-Medicare, anti-smoking regulation, anti-environmental protection, anti-federal social security, anti-campaign reform, pro-Iraq War, pro-mandatory minimum prison sentencing, Christian fundamentalist vice-president: Michael Richard Pence.

“Be careful what you wish for. You may receive it,” is an old saying – one that we would do well to remember as we pick over the tea leaves. And pray perhaps that, faute de mieux, the Democrats can find a new

version of John F Kennedy: a leader who will inspire his fellow Americans to pull together, not apart; to adapt to, not flee, the realities of the modern world, be they environmental, economic, scientific or political; to pursue greater equality, not less. And to work with, not against, America’s long-time coalition allies such as Nato to safeguard the security of the world.

Nigel Hamilton is a senior fellow at the John W McCormack Graduate School of Policy and Global Studies, University of Massachusetts. He is the author of “American Caesars: Lives of the US Presidents from Franklin D Roosevelt to George W Bush”