In a February 2018 budget memo to Congress, bureau officials wrote that under federal law, they were obligated to pay for a prisoner's "surgery" if it was deemed medically necessary. Still, legal wrangling delayed the first such operation until 2022, long after Mr. Trump left office.

"Transgender offenders may require individual counseling and emotional support," officials wrote. "Medical care may include pharmaceutical interventions (e.g., cross-gender hormone therapy), hair removal and surgery (if individualized assessment indicates surgical intervention is applicable)."

The Bureau of Prisons is the only federal agency under court order to provide gender-related surgeries. But the number of inmates requesting such operations within the bureau is minuscule, with only two known surgeries approved via court action.

The amount the bureau has spent on hormone therapy was also very small - ranging from $60,000 to $95,000 a year during Mr. Trump's term, according to internal department estimates obtained by The New York Times.

The Trump ads, which have been running in several battleground states - often during events with high male viewership, like football games - focus on a response by Ms. Harris to a question about transgender care for incarcerated people on a 2019 American Civil Liberties Union candidate questionnaire.

In her answer, Ms. Harris told the group that she "pushed" the state corrections department "to provide gender transition surgery to state inmates" while serving as California attorney general from 2011 to 2017.

"I support policies ensuring that federal prisoners and detainees are able to obtain medically necessary care for gender transition, including surgical care, while incarcerated or detained," she wrote. "Transition treatment is a medical necessity, and I will direct all federal agencies responsible for providing essential medical care to deliver transition treatment."

Initially, Ms. Harris represented the California Department of Corrections and Rehabilitation in its refusal to provide gender-affirming surgery to an offender convicted of murder who was born male.