Sanders is certainly doing better with non white voters than he did last time but can you point to the evidence that he has a commanding lead among minorities? Most of the data I have seen (although admittedly from dastardly corporate media!) suggest he does well with young voters of all ethnicities but struggles with older voters - who despite being less politically astute do have the sense to know their views only come close to counting if they register and vote
Perhaps Biden’s not going to able to limp to South Carolina after his poor showing so far but he is currently in a commanding lead there with Sanders, Steyer and Warren trailing well behind.
RealClearPolitics - Election 2020 - South Carolina Democratic Presidential Primary
www.realclearpolitics.com
Nevada is going to be the first test of the actual appeal of the candidates to non white voters - Sanders is currently doing better there and it is a caucus state after all where he has historically been stronger but Biden, at least for now, is ahead although polling has been sparse.