It is possible to be diplomatic and honest about Biden's mental faculties, especially after the disastrous debate with Trump.
Most especially when pressure ratcheted up on Biden to drop out - donors flexing financial muscle always works well. Especially after Biden became defiant. This was not a man putting the United States first.
But Keir would have known the media would have continuing to ask him that line of questioning on Biden. It's a major story. Honesty would have been the better route for him long term and I've no doubt the people would have supported him more if the media then tried to distort it.
Unfortunately for Keir, the media will now be waiting for other comments from now on where its possible to call his judgement into question.
You cannot viably have a situation where you've no idea if the US President is going to have a good or a bad day. Especially as things change rapidly in politics at that level with some very serious issues that require immediate urgent attention/decisions.
People need to have confidence in their leaders' ability to deal with any problem and to also have confidence in their ability to judge situations.
As for the UK's reputation, hasn't our reputation not been highly regarded for quite some time now?
Still, interesting to note the immediate defensive posturing in relation to Keir's comment aging as well as curdled milk! It's clear it hasn't aged well.
Hopefully, Keir's team game plans other situations better than this one in future.