Washington DC - Vice President Kamala Harris praised President Joe Biden's "patriotic" decision not to seek reelection Sunday and vowed to win the Democratic nomination and defeat Donald Trump.

"With this selfless and patriotic act, President Biden is doing what he has done throughout his life of service: putting the American people and our country above everything else," she said in a statement.

"I am honored to have the president’s endorsement and my intention is to earn and win this nomination," she continued.

"I will do everything in my power to unite the Democratic Party – and unite our nation – to defeat Donald Trump."

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For years Kamala Harris faced criticism that she was not up to the job of being a heartbeat away from the presidency. Now, she finds herself feted by Democrats as their best hope to stop Trump's comeback.

Despite blazing a trail as the first woman, Black, and South Asian vice president in US history, the 59-year-old Democrat long struggled with approval ratings as bad or worse than President Biden's.

The last 12 months, however, have revealed a transformed Harris.

And with Biden's endorsement of Harris after stunning the world by dropping his own reelection bid Sunday, she's suddenly on the cusp of history.

A child of immigrant parents – her father was from Jamaica and her mother from India – Harris grew up in Oakland, California, in an activist household that saw her attend her first rallies in a stroller.

Her focus on rights and justice saw her build an impressive CV, becoming California's first Black attorney general and the first woman of South Asian heritage elected to the US Senate.

Harris then went up against Biden in the 2020 primaries. In one stinging attack, she criticized him for allegedly opposing the bussing of students to segregated schools.

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"There was a little girl in California who was part of the second class to integrate her public schools, and she was bussed to school every day. And that little girl was me," she said in a barbed attack on her future boss.

But as his running mate, she consolidated the coalition that helped defeat the incumbent Trump in 2020.

Her transition to the White House, however, proved difficult as critics said she was underwhelming and gaffe-prone in a job that has been known to flummox many officeholders.

Struggling to carve out a role, she was tasked by Biden with getting to the roots of the illegal migration problem – but fumbled and then got defensive in response to a question during a visit to the Mexican border.

Unusually high staff turnover fed rumors of discontent in the vice presidential office.

And Republicans relentlessly targeted her as being unfit to take over should the worst happen to America's oldest-ever president, often resorting to stereotypes her supporters branded as sexist and racist.

Harris told the Wall Street Journal in February, "I am ready to serve. There's no question about that."

Things began to change as the 2024 race got underway.

The Biden campaign repeatedly deployed her to battleground states to hammer home the party's message on abortion rights, with Harris becoming the first vice president to visit an abortion clinic.

Gradually, she began to draw warm and fired-up crowds.

Some of the outreach was, however, widely seen as cringe-worthy. Earlier this year, she was mocked after she told chat show host Drew Barrymore her family sometimes called her "Momala," and Barrymore replied, "We need you to be Momala of the country."

But voters seemed to be switching on.

A clip of her quoting her mother as often saying "You think you just fell out of a coconut tree?" became a meme, with a rising sense among supporters that now could be her time.

If elected, Harris would break one of the highest glass ceilings left for women in the US – that of occupying the country's top office.

Her husband, Douglas Emhoff, would also be breaking new ground, moving from being the current Second Gentleman to the country's first First Gentleman.