With a burst of executive orders, President Joe Biden served notice Thursday that America’s war on COVID-19 is under new command, promising an anxious nation progress to reduce infections and lift the siege it has endured for nearly a year. At the same time, he tried to manage expectations in his second day in office, saying despite the best intentions “we’re going to face setbacks.” He brushed off a reporter’s question on whether his goal of 100 million coronavirus shots in 100 days should be more ambitious, a point pressed by some public health experts.