He has diminished America’s place in the world in a way that not even his most unheeding, volatile predecessors could have imagined.
That Mr Trump has torn up the rule book is disturbing enough, but that he has done so without offering anything that looks remotely like a viable alternative is chilling for the countries that once looked to America as a protective ally sharing common principles.
Mr Trump’s bull-in-a-china-shop leadership has also encouraged those whose ambitions were constrained if not curtailed by America.
In his excesses, they scent a weakness, an instability that may mean that America’s international authority, moral or military, may soon be historical. They are ready to exploit that vacuum.
Mr Trump has rejected the Paris climate change agreement shared by nearly 200 countries and put the rewards of a worldwide clean energy economy beyond those who believe his Make America Great Again guff; he has abandoned the Trans-Pacific Partnership, affording China the chance to consolidate its ranking as the dominant economic force in Asia; he has distanced America from the defence pacts that have underpinned transatlantic security since 1945, thereby forcing Europe to face threats like Russia on its own; he has told repressive states he did not care how they treated their citizens, provoking attacks on the opposition in Bahrain and Egypt and — all in less than six months — he has corrupted public discourse by lying about media outlets that challenged him by describing them as “fake news” organisations.
He has deepened division in America and, if all of that was not bad enough, he has brought narcissism to a new nadir.
Even by the standards of a post-colonial tinpot despot drunk on achieving absolute power, that is a spectacular rampage. But how for long can it continue?
Though it is too early to say so definitively, yesterday’s testimony to the Senate by the former FBI chief James Comey, who was fired by Mr Trump, may in time be seen as the moment the Trump presidency was holed below the water line.
Mr Comey testified that Mr Trump asked him to drop his investigation into the former national security adviser Gen Michael Flynn. He also described how Mr Trump pressurised him to shut down an investigation into an adviser’s links with Russia.
If these allegations are accepted, and there seems no reason to imagine that they will not be, then the president could face charges of trying to obstruct the course of justice. If he is found guilty he could be impeached.
Though that is an attractive proposition, and even if the prospect of a Pence presidency is more than sobering, the prospect of impeachment might distract Mr Trump and curtail his wildest decisions.
That these are the hopes the world must cling to for the next four years is a measure of how deep and dark this tragedy has become.