Yes, this is unique; 1912 last example of two candidates who have been elected President.
This limits the usefulness of historical examples, but that does not imply that the opposite of the trend is true. 2020 is the clearest analog imo: unpopular incumbent running against politician with national experience.
Close polls are simply not predictive at this stage.
This is Biden's decision. Forcing him out makes it worse for Dems.