Why are either legitimate? If POTUS is illegitimate, the VP is too. It’s a package deal.
My observations along that line:
Both were confirmed, separately, by Congress and sworn in separately.
Harris ALWAYS flies on AF2, Joe NEVER flies on AF1.
Call signs are given by Military Air Command when the flight plan is filed...you can’t \request\ a callsign.
With this understanding, I have concluded that Harris is legit as VPOTUS.
Biden is legit as POTUS.
The US military command does \not\ recognize Biden as Commander-in-Chief.
Biden has to know this.
That can explain why he is so slow to act in military endeavors and also why many of his military acts fail spectacularly (cf; Afghanistan and the Gaza Pier).
He must get permission first.
I have other extended thoughts concerning the C-in-C but I’ll leave those for later.