I think that’s a flawed distinction. The difference between Biden and Trump in terms of domestic and foreign policy that is actually likely to be carried out is less dramatic than the difference between Bernie and Biden. Biden, like Trump (despite his rhetoric), would be just fine proceeding with the neoliberal consensus whereas Bernie would pose an actual threat. Trump is ‘far right’ because of his nationalist rhetoric. But he’s carrying out the will of mainstream Republicans on both foreign and domestic matters.
I’m not making the ridiculous suggestion that there is ‘no difference’ between Trump and Biden. Just that it is smaller in practice than between Biden and Bernie.
Also, I’m sure some Bernie voters will go Trump again out of spite if he loses. Others will go Trump because they view Biden as more dangerous to the existence of the Left in the long run, so it’s really a political strategy. Obviously both are totally callous and brain dead positions. Millions do not have the luxury to worry about long run strategy. The difference between a 10% boost and 15% cut to some social program is the difference between eating and going hungry for many people.