'My uncle knew the Unabomber.' What makes Trump say such strange things?

Donald Trump's bizarre public behavior - which this month has included him claiming, wrongly, that his uncle knew the Unabomber, and ranting unprompted about windmills on his recent trip to the UK - have once again raised questions about the president's mental acuity.

- Adam Gabbatt

Trump, 79, frequently exhibits odd behavior at campaign events, in interviews, in spontaneous remarks and at press conferences. He repeatedly drifts off topic - including during a cabinet meeting this month when he spent 15 minutes talking about decorating - and seems to misremember simple facts.

During his time as US president, Joe Biden was subjected to intense speculation over his mental acuity, including from Trump. A disastrous debate performance in June 2024, when Biden visibly struggled to maintain his train of thought, eventually led to him not seeking re-election.

Trump, however, has largely been spared the same scrutiny, despite instances of odd behavior throughout his second term.

Last month, at a meeting with Ursula von der Leyen, the European Commission president, Trump abruptly switched from discussing immigration to say: "We will not allow a windmill to be built in the United States. They're killing us. They're killing the beauty of our scenery."

He continued non-stop and unprompted, for two minutes, claiming without evidence that wind power drives whales "loco" and "kills the birds" (in fact, the number of birds killed by wind turbines is tiny compared with the number killed by cats and power lines).