It was early in Joseph R. Biden Jr.’s vice-presidential search when he asked his advisers a sensitive question about Senator Kamala Harris. He kept hearing so much private criticism of her from other California Democrats, he wanted to know: Is she simply unpopular in her home state?
Advisers assured Mr. Biden that was not the case: Ms. Harris had her share of Democratic rivals and detractors in the factional world of California politics, but among regular voters her standing was solid.
Mr. Biden’s query, and the quiet attacks that prompted it, helped begin a delicate audition for Ms. Harris that has never before been revealed in depth. She faced daunting obstacles, including an array of strong competitors, unease about her within the Biden family and bitter feuds from California and the 2020 primary season that exploded anew.
Though Ms. Harris was seen