What's behind alarming new US outbreaks?

As coronavirus outbreaks are slowly brought to heel in many places around the world, the US is among a handful of countries facing a surge of new infections.
More than two dozen states are now seeing increases in new cases over the last 14 days.
Of these, Texas, Florida, Arizona and California have emerged as the country's latest virus epicentres.
But while cases are clearly rising, state leaders and health experts are divided on the cause.