This is pretty accurate. I come back to this time and again - the way the Pod Bros are acting, you’d think they’d been calling for Biden to step down since the campaign began. They have not. At all.
AOC's perspective, abridged:
Voters already knew Biden was old before the debate, and had locked that in.
The sudden salience of the issue was the 'political class' of pundits, donors & partisans suddenly being forced to reckon with it too.