I was listening to the issue being explained by an American political journalist on a podcast recently.
She said the problem facing the Democrats is complex. Even if Biden does step down, finding his replacement is tricky. Apparently the funding for the Democratic campaign is for a ‘Biden / Harris’ ticket. So, Harris would have to be ‘on the ticket’; logically making her the candidate, but she’s unpopular with the electorate.
The journalist said it might just be possible (re. the funding issue) for someone else to run for the top job and leave Harris as VP. However, she said the presidential candidate always chooses their own VP running mate.
Of course, at the moment, it’s all a moot point because Biden is still the Democratic candidate. Phew🤷♀️