SILVER SPRING, Md. (AP) — Coronavirus outbreaks are testing the public health networks in pockets of the U.S., while some states prepare to lift lockdown measures, seeing signs of progress. From a hospital near the Navajo Nation to the suburbs of the nation’s capital, front-line medical workers in COVID-19 hot spots are struggling to keep up with a crushing load of patients. Governors are starting to slowly reopen some segments of their local economies, pointing to evidence that COVID-19 deaths and new hospitalizations are peaking or starting to recede. But a government whistleblower warned Thursday that the U.S. faces its “darkest winter in modern history” unless leaders act decisively to prevent a rebound of the virus.