US Representative Nancy Pelosi has called Biden a "patriotic American" who has always put US first and expressed gratitude to him for always believing in the promise of America.
The process of selecting a new nominee remains uncertain, but an increasing number of Democrats believe that any transition would likely culminate swiftly with Harris assuming the mantle.
Trump returned to the campaign trail in Michigan's Grand Rapids, days after accepting the Republican nomination for president at the Republican National Convention.
Australia all-rounder Sophie Molineux could be in a race against time to get fit in time for the New Zealand series before the Women's T20 World Cup after she suffered a fractured rib.