While the mainstream media have sought to downplay the impact of 2020 party conventions, polls showing President Donald Trump surging ahead as the Democrats held their virtual rally have them both stumped and spinning. “Don’t be surprised if Biden doesn’t get a convention bounce in the polls. That’s not the point,” declared an early Friday headline in the Washington Post. Post-convention surges are hard when the country is polarized and the parties “stage theirs back to back, as they will this year,” argued opinion writer Karen Tumulty. Except both things were just as true in 2016, which didn’t stop the...