One key sign was what didn’t happen: 0bama didn’t endorse Joe. Whatever kept that from happening, and there were probably several things - too old, too corrupt, too bland, no programs, no passion, and obviously declining mentally - whatever that was, was the watershed.
IOW ...most of the reason he made him his VP in the first place.
Why endorse a loser. Reagan didn't endorse Bush until it was clear he would be the nominee, even Reagan knew Bush would not make a great President.
I suspect Obama knew about the Biden Crime Family when he was "told" to take Joe on as his VP to keep the status quo oiled. My guess is Obama didn't endorse Joe for obvious reasons; the Obama's have their own agenda, or had.