The most important thing is of course the electoral college, which currently looks promising for Biden, all he nees to do is hold the states Hillary won (easy peasy) and win back the rust belt, which imo is going to be easier for him to do than it was for Clinton. Here are some reasons for that:
1. His performance in the democratic primary indicates his strength in Michigan, Penn and Wisconsin. The reason is that Bernie won against Clinton in Michigan, and yet Biden beat bernie this time around by quite a large margin. This seems to imply that Michigan may have gone to Trump because of the anti hillary wave during the primary - the state seems to highly prefer Biden over Clinton. If that's true, lets keep in mind how hated Clinton was during 2016 and the seeming respect Bernie and Biden have for each other, perhaps the split in the democratic party will not be as sevre this time around, especially because the primary season seems to be much shorter now.
2. Someone already mentioned the possible implications of coronavirus, if the economy continues to wobble, it will be a massive blow to Trump.
3. His home state - Pennsylvania, which could help his appeal in the rust belt further.
4. Biden seems to be considering Michigan's governor as his running mate, her recent fight with Trump over corona seems to be really helping her appeal in that state and assuming he picks her, its possible Biden can use that support to help win Michigan.
5. Biden isn't Clinton - russian hackers and trump had plenty to milk, from Benghazi to her e-mails to Bill clinton and so much more. There simply isnt any major scandal Biden has endured, I see hardly anything Trump can use against him other than "sleepy joe," he can't dare use the age argument that can backfire a lot too.
And finally my own personal thoughts - USA has very unfortunately had to go through a term of a drama queen reality tv style president that has made idiotic, nonsensical statements and decisions. I'm tired of the drama, he used to be entertaining in the beginning but now the joke of his presidency isnt even funny anymore - specifically looking at corona. For anyone wondering, research his prior statements about it and how slow he was to act just so he could attempt to salvage the economy to use it as a card in the election. What a pathetic president. Get rid of him Biden, please.
I'm aware Biden isn't the ideal candidate, he isn't as sharp as he once was and the years have worn him down. But his experience, compassion and decency is something I long for in American politics, to stop this partisan bickering or at least help to alleviate it. To finally stand up to China instead of plastering worthless tariffs only for the CCP to send unfinished products for final assembly in Vietnam and then to the USA to bypass them. USA's international reputation has seriously tanked, and i'm just scared for the future. I don't want to live in a social credit authoritarian dystopia like china all because the world was too focused on drama queens like Trump, and not the looming threat in the east.