Donald Trump’s frequently bizarre public appearances, which this month have seen the president claim, wrongly, that his uncle knew the Unabomber and rant unprompted about windmills on his recent trip to the UK, have once again raised questions about his mental acuity, experts say.

For more than a year Trump, 79, has exhibited odd behavior at campaign events, in interviews, in his spontaneous remarks and at press conferences. The president repeatedly drifts off topic, including during a cabinet meeting this month when he spent 15 minutes talking about decorating, and appears to misremember simple facts about his government and his life.

Over the weekend Trump, during a meeting with the European Commission president, Ursula von der Leyen, abruptly switched from discussing immigration to saying this: “The other thing I say to Europe: ​we’ve – 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.”

Trump proceeded to speak, non-stop and unprompted, for two minutes about windmills, claiming without evidence that they drive whales “loco” and that wind energy “kills the birds” (the proportion of birds killed by turbines is tiny compared with the amount killed by domestic cats and from flying into power lines).