WASHINGTON — In early March, Joe Biden’s presidential campaign unfurled a public health advisory committee composed of half a dozen heavyweight experts to advise on how best to operate a campaign on a trail that was becoming increasingly dangerous as coronavirus infections spread across the country. The announcement was seemingly designed to, as the New York Times characterized it, “project calm and competence” less than a week after the Trump White House began its chaotic and often antagonistic daily briefings. There was a perception that Biden, in contrast, would have a foil group - a former surgeon general for every...