Theres only one real chance to defeat the incumbent in a race like this and its because of recession or a significant pattern of retraction such as 4% of deaths for cases if Corona were widespread (and the worst case scenario). So yes, I think its a wild card factor that could put from us from unlikely (Trump was very unlikely in his progression) into the seemingly extreme such as Sanders. I count it as a possible maybe.
I dont think 4% should happen, just washing hands alot is not a big ask. I reckon it could play out as 1% over normal flu deaths which is still bad enough but for an economy or altering elections maybe not enough.