It was December 2003, a final debate in the final days before the runoff election in Kamala Harris’ race for San Francisco district attorney against her onetime boss, Terence Hallinan. And Hallinan, the crusading progressive incumbent, was going low: Harris could not be trusted to prosecute city corruption, he suggested, because of her relationship with Willie Brown the outgoing mayor, peerless local kingmaker and Harris supporter whom she had dated years earlier. “He has an interest,” Hallinan speculated, “in having a friend in the district attorney’s office.”

Harris conjured a different hypothetical. She would take on crooked actors of all kinds, she said. In fact, she already had a prospective target in mind.

“San Francisco is the bluest of blue,” said Tony West, her brother-in-law and longtime informal adviser. “All political wars there are civil wars. And so it’s like a family fight. And those are often the worst.”

For Harris, who was 38 when she ran for district attorney, the campaign arrived at an inflection point a period of restlessness, according to former colleagues, in the career of a hard-charging deputy accustomed to straddling disparate orbits.

Sixteen years on, as a California senator seeking the Democratic nomination for president, Harris is not, by her own admission, the candidate of structural upheaval, like Sens. Bernie Sanders of Vermont or Elizabeth Warren of Massachusetts. She is not an old-guard centrist, like former Vice President Joe Biden. But in a party weighing how best to counter President Donald Trump’s boundless capacity for brawling, Harris is the one who knows how to hit hardest, friends said, because that is how you win in San Francisco.

After a decade of unglamorous work for local prosecutors and a studied induction into San Francisco’s social elite, Harris was by turns a society-page veteran and a prolific loiterer at supermarket parking lots, unfurling an ironing board from her back seat as a canvas for campaign literature. She began her evenings at fundraisers in ritzy Pacific Heights and ended them at the modest apartment where she lived alone in the city’s SoMa neighborhood, stretching across her living room floor to compose longhand thank-you notes to donors.

“She was always the candidate who was like, ‘I got everything done on my list. Did you get everything done on your list?’” said Jim Stearns, a top consultant to Harris in 2003.