Two decades later, as Ms. Harris concludes another barrier-breaking run, Ms. Prozan and other aides who worked on the vice president's first campaign say they see the same underdog grit and discipline she displayed in her inaugural race.

"She is tireless. She's relentless," Ms. Prozan said. "She's a good closer."

The parallels between Ms. Harris's first campaign and her current one are striking, and provide insight into how she has come within touching distance of the presidency. She has employed much of the same playbook she used in her race for district attorney: building a team at a rapid pace. Exceeding fund-raising targets. Trying to appeal to a broad coalition. Energetically reaching out to voters. And, on a personal level, tapping into guidance from her mother, who died in 2009.

"She's been here before," said Andrea Dew Steele, who was an aide on Ms. Harris's first campaign. "People are always underestimating her and her ability to do the hard work, and she always rises to the occasion."

"For starters," Ms. Dew Steele added, "she is not afraid of going against tough men."