The US vice president, Kamala Harris, rushed to the defence of Joe Biden after his calamitous debate performance against Donald Trump in late June. In an interview with CNN, she said: “There are three things that were true yesterday before the debate that are still true today … First, the stakes of this race could not be higher. Second, the contrast in this election could not be more stark. And third, we believe in our president Joe Biden, and we believe in what he stands for.”

But one in three Democrats now believe Biden should withdraw from the presidential race. And, in spite of her declaration of support, Harris is emerging as the frontrunner to replace the 81-year-old should he step aside.

A CNN poll published last week shows Harris within “striking distance of Trump in a hypothetical matchup” – 47% of registered voters support Trump compared with 45% for Harris. The vice president’s numbers centre on her broader appeal to women and independents.

As well as having been vetted for national office, and intensely scrutinised by the media and the Republican party, there is a degree of momentum building for Harris to replace Biden at the top of the Democratic ticket. There is also notable congressional backing.

Jim Clyburn, a prominent African-American congressman from South Carolina whose endorsement of Biden was critical to his nomination in 2020, told MSNBC on July 2 that he would support Harris to be the Democratic nominee should Biden quit the race.

Born in Oakland, California, on October 20 1964, Harris began........

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