U.S. cases of the new coronavirus grew to more than 430,000 Wednesday, as the country recorded its deadliest day yet.

There were 1,973 deaths from Covid-19 in the U.S. during the 24-hour period ended 8 p.m. Wednesday, according to a Wall Street Journal analysis of data from Johns Hopkins University.

In the previous 24-hour period, 1,939 people...