Certainly not the only difference, I should think!
I’d suggest that Biden’s “stupid” comments (as mentioned up-thread, often caught on tape) don’t indicate that he’s stupid. He’s is, IMHO, a very intelligent person. Like many Dopers, his intellect drives him to distraction (and verbalization) when he sees absolutely asinine bullshit around him.
I, for one, hate bullshit discourse. But if I’m at work and there’s someone in the room who will throw their pen in the air and say “this is fucking ridiculous,” the meeting becomes productive. I can definitely see Biden in a closed-door meeting with the Pres and asking “do you have the slightest fucking clue what you’re doing?”
A good leader keeps blunt counsel to call his bullshit. “The Emperor’s New Clothes” comes to mind.
Although, really - keep your damned mouth shut in public…