This article seems to implicate Biden's advisors in that Biden was on some kind of insane globe-hopping schedule leading up to his debate.
When not exhausted, he is said to remain an imposing presence:
"Aides present in the Situation Room the night that Iran hurled a barrage of missiles and drones at Israel portrayed a president in commanding form, lecturing Prime Minister Benjamin Netanyahu by phone to avoid a retaliatory escalation that would have inflamed the Middle East. “Let me be crystal clear,” Biden said. “If you launch a big attack on Iran, you’re on your own.”
Netanyahu pushed back hard, citing the need to respond in kind to deter future attacks. “You do this,” Biden said forcefully, “and I’m out.” Ultimately, the aides noted, Netanyahu scaled back his response."
https://www.seattletimes.com/nation-world/bidens-lapses-are-increasingly-common-according-to-some-of-those-in-the-room/