Joe Biden is planning a head-on acknowledgement of the country’s once-unimaginable loss — half a million Americans in the COVID-19 pandemic — in striking contrast to the approach of his predecessor.Confronting the grim milestone directly and publicly, Biden is trying to strike a balance between gravity and hope, while Donald Trump generally avoided constructs of collective grief for the deaths on his watch.Monday’s bleak threshold was playing out against contradictory crosscurrents: an encouraging drop in coronavirus cases and worries about the spread of more contagious variants.