Former US Vice President Kamala Harris has expressed concern that she did not ask Joe Biden to pull out of the race for the White House.

In an interview with the BBC for Sunday with Laura Kuenssberg, she said: "I do reflect on whether I should have had a conversation with him, urging him not to run for re-election."

After months of speculation about his health and mental acuity, President Biden ended his re-election bid in July 2024 after a disastrous performance in a debate against Donald Trump a few weeks earlier.

Harris, who stepped in as the Democratic nominee but lost to Trump, has revealed in her book about her three-month campaign that she did not discuss with President Biden her concerns over his ability. Nor did the then 81-year-old raise the issue with her.

In the book, 107 Days, the former vice-president wrote that Biden's decision to run again was a choice that shouldn't have "been left to an individual's ego, an individual's ambition". She wrote that "perhaps" she should have raised it with him.

In this interview, she told the BBC that she still ponders whether she should have acted differently and talked to him about it.

"I do reflect on whether I should have had a conversation with him, urging him not to run." She said, "My concern, especially on reflection, is, should I have actually raised it?". She questioned whether it was "grace or recklessness" that stopped her speaking up.

Her worry, she added, was not Biden's capacity to do the job of commander in chief but about whether he would meet the demands of a gruelling election campaign to stay in the White House.

When pressed on why there is a distinction, she said there was a serious difference between running for the office and conducting the duties of being president. And running against Trump is even more demanding, she said.

She said she had a "concern about his [Biden's] ability, with the level of endurance, energy, that it requires, especially running against the current president".

The former vice-president said it was hard for her to speak up because she risked being accused of promoting her own political interests if she had confronted Biden about his health.

"Part of the issue there was that it would – would it have actually been an effective and productive conversation, given what would otherwise appear to be my self-interest?"

The issue of whether more people in Biden's circle could have challenged him about the wisdom of his running again has become a major talking point.

One book, Original Sin by Jake Tapper and Alex Thompson, alleged that people close to him covered up his physical deterioration from the public.

Biden's aides have pushed back at the allegation, saying there were physical changes as he got older but no evidence of mental incapacity and nothing that affected his ability to do the job.

In his first interview after leaving the White House, in May of this year, Biden told the BBC it would not have mattered if he had left the race any earlier.

His former vice-president is in the UK promoting her new book. In a wide-ranging conversation on Sunday with the Laura Kuenssberg programme, Harris also said it was "possible" she could run for the White House again.

She has already ruled out running for governor in her home state, California, and the former prosecutor told the BBC she was "not done" with public service.