If President Biden doesn’t run for re-election in 2024 and Harris ISNT the 2024 nominee does that mean the Biden administration was a failure/disappointment? And does it almost assure the GOP that they’ll return to the White House?
No but it will make it significantly more likely as defeating an incumbent president isn't an easy feat, I mean after everything that he did over the course of his presidency even Trump got relatively close to being re-elected.
But even if Harris is the nominee the GOP stands a much better chance at defeating her than they would Biden as the incumbency bonus doesn't really translate all that well to the VP.