probably 20 years ago and it was remarkable how lucid he was and how well he spoke, not the rambling somewhat chaotic speech patterns he has now. this is an interesting article from 2017 about his speech changes even at that time. before anyone gets triggered, it states it could be normal aging and not necessarily cognitive decline but there are clear differences.
https://www.statnews.com/2017/05/23/donald-trump-speaking-style-interviews/