Nobel laureate Paul Krugman has accused Donald Trump of 'clearly and undeniably' losing his mind and renewed his warning that the president is 'sundowning.' Krugman made the comments in a Substack post published on 23 September, a day after Trump's address to the United Nations General Assembly.
The 2008 Nobel Prize winner in Economic Sciences made the remarks after Trump announced during his UN address that US government documents would refer to artificial intelligence as 'Super Intelligence'. The State Department subsequently instructed employees in its Bureau of International Organization Affairs to use the term in official communications.
Krugman first used the 'sundowning' comparison in January 2026. The term is commonly used to describe increased confusion, agitation or behavioural changes that can occur later in the day, particularly among some people with dementia. Krugman's use of the term to describe Trump is his own characterisation and is not a medical diagnosis.
He repeated the warning in his latest post, arguing that he had seen no reason to change his assessment of Trump's behaviour.
Krugman's 'Mad King Donald' Warning
Writing on his Substack newsletter, the former New York Times columnist said most coverage of Trump's UN speech missed what he considered the larger story. Instead of focusing on the president's rejection of global cooperation or disputed claims in his remarks, Krugman argued that Trump's mental state was the greater concern.
'Isn't the bigger story the fact that the leader of what used to be the world's most powerful nation, I say 'used to be' because America's power is collapsing before our eyes has clearly and undeniably lost his mind?' he wrote.
Krugman pointed to Trump's demand that the term 'artificial intelligence' be scrapped because 'the use of the word artificial makes intelligence fake, it makes it sound fake'. Trump told the General Assembly that US government documents would henceforth refer to AI as 'Super Intelligence'.
The Associated Press reported that the State Department subsequently instructed employees in its Bureau of International Organization Affairs to use 'Super Intelligence' instead of 'Artificial Intelligence' in documents, positions, remarks and press materials.
Krugman argued that Trump's approach makes him more dangerous, particularly if Republicans lose control of Congress in the midterm elections. Even with reduced legislative power, he warned, 'Mad King Donald' would not accept responsibility for a political defeat.
'He won't feel that he has failed America, he will believe that America has failed him and try to punish the nation accordingly,' Krugman wrote.
What Happens Next
Krugman also argued that if Democrats win the White House in 2028, they could inherit what he described as 'a badly damaged nation'. His assessment rests on his view that Trump could turn against political opponents and the broader public if he believes the country has rejected him.
The economist's comments came as Trump's UN address drew attention for its rejection of international AI regulation and his proposal to refer to artificial intelligence as 'Super Intelligence'.
'The very same people who said we'll all be dead in 12 years because of global warming... are now saying that AI is going to kill us all, that robots are going to attack us, and that everything is going to be a total disaster,' Trump told delegates.
Trump also framed AI development as a race, saying 'whoever wins super intelligence wins' and claiming the US holds a large lead over China. He pledged Washington would 'only encourage superintelligence' and not restrict its growth, dismissing safety advocates as alarmists.
Krugman's comments are his interpretation of Trump's public behaviour and do not constitute a medical assessment of the president. There is no evidence in his post establishing a medical diagnosis or cognitive disorder.
His remarks nevertheless provide a direct account of how the economist interpreted Trump's UN speech and its wider implications.
Krugman argued that Trump's response to a potential loss of political power could be punitive towards both his political opponents and the broader American public, but that remains his prediction rather than an established outcome.
