How to explain it? Stress? Exhaustion? After all, Boris Johnson has had a pretty tough week. He lost his majority. He lost his first three votes as Prime Minister.

He failed to secure the general election he’d pretended not to want. More than 20 of his MPs rebelled against him, and were then kicked out of his party, prompting a backlash from those who remained. And then on Thursday morning, to cap it all, Jo Johnson – his own brother – resigned out of the blue as one of his ministers.

So yes. Reasonably gruelling. But even so – I’m not sure it can entirely account for what happened on Thursday evening. Because, at a police training centre in West Yorkshire, Mr Johnson gave unequivocally the most bizarre performance of his career.

Then again, performance isn’t really the word, because performances are deliberate, and this, all too plainly, was not. Having arrived well over an hour late, Mr Johnson stumbled up to his lectern and began what should have been a straightforward speech trumpeting his latest pledges on crime. Somehow, though, he didn’t seem to be entirely himself.

We’ve all seen Mr Johnson bumbling and burbling for comic effect. It’s what he does. He’s been doing it his entire political life. But this wasn’t like that. Here, he looked genuinely dazed. Absent. Distracted. Lost. He spoke slowly, vaguely, and with long, inexplicable pauses – as if, while he murmured away, his mind kept straying on to some other, rather more troubling topic.