The virus that ravaged Northeastern U.S. cities is surging through Southern and Western states. It’s different this time. Younger people are getting sick with Covid-19. States that had brief coronavirus lockdowns are struggling to encourage social distancing and mask-wearing. Many people appear to have embraced their usual summer rituals. Health officials are sounding alarms about a surge in cases racing not through nursing homes, but bars and house parties. Hospitals are filling with medically-vulnerable elderly—but…