It's not worth anything. I don't know where people get this idea that someone's "real" persona consists only of the things they say in intimate private settings. A guy who runs around saying things he knows aren't true and calling people names is a liar and a bully, even if he understands himself to be playing some kind of role or acts politely in 1:1 conversations with Bill Maher.
Depending on the personae (is that a word?), it would be pretty clear, no? If one is really stupid and one is brilliant, how would the brilliant one be an act? If you can act brilliant, you are brilliant.
Reminds me of a story told by someone who was an intern or assistant for a politician (or consultant?) way back in the day before social media. They recount their first experience watching the politician at a town hall - they were late and apologetic, and gave a speech that was funny, compelling and authentic and the crowd ate it up.
They attended the next town hall, and the principal was late again, and proceeded to give the same speech, beat for beat. The same routine was repeated dozens more times at dozens of locations with different audiences, save for the politicians staff. In truth, the politician was not as funny or as sincere as the practiced speech and routine made them seem.
All this to say; acting funny or brilliant behind closed doors without cameras rolling doesn't mean you actually are those things. It's easy to recycle the same schtick after years of honing it and figuring out what works and what doesn't, Trump has impeccable showman instincts.
With Johnson I at least had the impression that he understood the showmanship aspect of it really well. Less so with Trump, at least it seems less polished.
It indeed was Boris - thank you! It's weird to compare my faulty recollection to the actual account; only 2 occasions narrated, not dozens - though it is implied, and the narrator wasn't an intern.
Trump seems to be a stupid person's ideal of what 'brilliance' is. So... his acting as brilliant is their version of brilliant, regardless of anything else. He is their alternative fact.