WILMINGTON, Del. — The final stretch of a presidential campaign is typically a nonstop mix of travel, caffeine and adrenaline. But as the worst pandemic in a century bears down on the United States, Joe Biden is taking a lower key approach. Since his Aug. 11 selection of California Sen. Kamala Harris as his running mate, Biden has had 22 days where he either didn’t make public appearances, held only virtual fundraisers or ventured from his Delaware home solely for church, according to an Associated Press analysis of his schedules.