Ms Harris, 59, quickly garnered support from enough party delegates to win the nomination at the Democratic National Convention next month.
Since taking office in 2021, Ms Harris has participated in several international summits and bilateral visits with the UK, including an AI summit convened by Rishi Sunak last November.
Officials who worked with her said that she knew much less about AI than other figures in the US government, and failed to impress her counterparts at the summit.
“She seemed pleasant enough, without being wildly exciting,” a former UK aide who met her at the event told The Telegraph.
“Hillary Clinton had real charisma and she didn’t have any of that star power.
“Gina Raimondo, the US commerce secretary, was also far more impressive – more across detail and more confident.”
At the summit, Ms Harris reportedly angered Downing Street by playing down the “existential” risks of AI, which Mr Sunak’s administration had tried to emphasise.
Her speech contained a section on AI “threats that are currently causing harm”, which was not the intended focus of the gathering.
The remarks were interpreted as a rebuke to the UK government, and as an attempt to upstage Britain at its own summit, sources told Politico. She held her speech at the US Embassy, away from the main event at Bletchley Park, and arrived in a 20-car motorcade.
“People in No 10 weren’t delighted about her speech,” one aide told the outlet.