It's a sad day, but a day that also gives us hope
There was no way Biden could win. The age issue was insuperable. It was omnipresent. You could not mention his name to a single voter without it being part of the conversation. Now that age issue is squarely on Trump. He would be older than Biden is now by the time he finished another term.
Joe has endorsed Kamala, and that gives her a very strong position to claim the nomination. It's not guaranteed though and I can think of a few candidates who would be better. Joe's endorsement can also be viewed in the lens that he had to endorse her to show loyalty and honor for his VP. Regardless, she is still light years better than Trump.