I'm nervous. Biden was a flawed candidate, but he already beat Trump once and had the incumbent advantage. Harris was a very unpopular candidate in 2020, and it's unknown if any other candidate will do better against Trump. But since Biden chose to do this, there's no doubt he made the right decision for him.
As far as I can tell based on articles I've read, he really wanted to run, but the party was getting divided over calls for him to step down. He must have figured that the infighting would take away his incumbent advantage
Possibly, but the fact that he was actually willing to step down means he doesn't have it in him to keep this up for 4 more years. Let's hope America repeats 2020 instead of 2016.