A CDC survey of 5,412 people in late June found that 31 percent were experiencing symptoms of anxiety and depression, about three times the number of respondents who said the same in the first two quarters of 2019. Another 26 percent reported symptoms of a trauma- or stressor-related disorder. Eleven percent of people said they had seriously considered suicide in the previous 30 days. Now some researchers are asking if stress — especially chronic stress — might be another preexisting condition that makes Covid-19 infections worse.