The key difference between Donald Trump’s first and second presidencies can be summed up by his two official portraits. The first after his victory in 2016 shows a smiling Trump, probably delighted to have won against the odds and, at least in theory, willing to work with his opponents.

The second shows a more brooding figure glaring into the camera – a man who recognises that a sizeable chunk of the country is never going to like him and does not care. This second image encapsulates what I see as the twin themes of Trump’s second term: revenge and legacy.

In 1973, American political scientist Arthur M. Schlesinger Jr introduced the concept of the “imperial presidency”. He argued that the separation of powers that lies at the heart of US democracy had become overbalanced under the presidency of Richard Nixon in favour of the executive branch.

In response to the Vietnam war and the Watergate scandal, where operatives working for Nixon bugged the Democrat National Committee’s headquarters and he tried to cover it up, Congress reasserted itself. The war powers resolution of 1973, for example, required the president to consult with Congress before committing US armed forces to conflict.

The Obama administration also shows how effectively a president’s agenda can be derailed when one party puts its mind to it. Republicans blocked Obama’s appointments to the judiciary and significantly watered down his main achievement, the Affordable Care Act.

However, Trump’s second administration has seen the imperial presidency reach its peak. He has wielded this power against his political enemies, whether other........

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