Joe Biden, who is poised to earn enough delegates to formally secure the Democratic presidential nomination this month, promises to enter the general election campaign on offense in states President Trump won in 2016. As the nation battles a pandemic, high unemployment, and civil unrest, polls show Biden leading Trump in six critical swing states the latter narrowly carried four years ago: Florida, Michigan, Pennsylvania, North Carolina, Wisconsin, and Arizona, according to CNBC/Change Research poll conducted in mid-June. Observers note that the battleground advantage polls came shortly after a Gallup poll showed that Trump's net approval rating had dropped 19...