MARK HALPERIN: Kamala battles to regain momentum after late-summer swoon

Before she became her party’s nominee for president, Kamala Harris had not made a substantial, discernable positive public impact during her nearly four years in the White House. She largely operated under the radar and fell short regarding some of her most high-profile assignments. 

She had not universally distinguished herself as a leader. She had not won over swaths of new fans. She had not fully earned her place as next in line. She was known more in Washington circles for her rocky...