Chicago (AFP) - Kamala Harris will pledge Thursday to be “president for all Americans” as she accepts the Democratic Party nomination before a rapturous crowd in Chicago in the biggest speech of her life.

A sea of waving Stars and Stripes flags and chants of “USA” filled the arena as jubilant Democrats prepared to anoint Harris as their standard-bearer against Republican Donald Trump.

The 59-year-old vice president was to lay out her personal story and vow a “new way forward” as she reaches out to voters after one of the most extraordinary turnarounds in US political history.

Pop megastar Beyonce, whose song “Freedom” has become the campaign’s anthem, was reportedly set to be a surprise warm-up act before Harris takes her star turn at the Democratic National Convention.

Country act The Chicks sang a version of “The Star-Spangled Banner” while pop star Pink also performed as the Democrats rolled out a list of celebrity backers.

“I know there are people of various political views watching tonight. And I want you to know: I promise to be a president for all Americans,” Harris was to say, according to excerpts released by her campaign.

The first Black woman nominee for a major party, Harris has electrified supporters in the wake of 81-year-old President Joe Biden’s shock decision to drop out a month ago.

She has quickly united the party, wiped out Trump’s lead in the polls, and raised staggering amounts of funds.

“You know what I’m really excited for?” said Amanda Taylor, a 47-year-old delegate from Missouri. “Of course, Kamala, but I hear maybe Beyonce is going to come!”

- ‘So proud’ -

Biden, who gave an emotional farewell speech to the convention on Monday, said he and First Lady Jill Biden had called Harris to wish her luck.

“I am proud to watch my partner Kamala Harris accept our nomination for president. She will be an outstanding president because she is fighting for our future,” Biden, who is on holiday in California, said on X.

Democrats are however trying to temper their hopes, knowing that Harris faces a tough sprint to a nail-biting election on November 5, which as in 2020 may be decided by a handful of votes in key states.

From Barack and Michelle Obama to Bill Clinton, senior figures have warned all week that Harris has a brutal fight on her hands to beat Trump.

Trump, 78y, believed he was cruising to a stunning return to power against Biden. Instead he has been unsettled by the sudden Democratic switch to a much younger opponent – and one looking to make history as the first female president.

The Republican is increasingly resorting to personal insults and race-baiting.

Speaking near the Mexican border barrier built during his presidency in the battleground state of Arizona, Trump focused Thursday on immigration, which Republicans believe is a major weakness for Harris.

Recounting stories of people he said were killed by migrants who had come across the border illegally, he said: “As Kamala gives her convention speech tonight, she will not mention the victims. She won’t even mention their names.”

- Kamala Vibes -

The sheer speed of Harris’s rise, from the first female, Black and South Asian vice president to the Democratic standard-bearer also means Harris remains somewhat unknown to US voters.

Harris will seek to remedy that in her speech. She will talk about being raised by a working, single mother, insisting the challenges facing families hit by inflation, a campaign official told reporters.

She will recount her career as a prosecutor, highlighting her fight for victims of sexual abuse and gun crime – and likely highlighting the fact that in Trump she now faces the first convicted felon ever to seek the White House.

Harris has been short on policy announcements since taking over as the Democratic standard-bearer, particularly when it comes to the economy, a key issue in the election.

“Voters already have the Kamala vibes. Now they need the Kamala agenda,” said Larry Sabato, a professor at the University of Virginia.

For now, Democrats appear happy to ride a tidal wave of joyful vibes, putting behind them the despair over Biden’s catastrophic debate performance against Trump and the disputes over whether he should stay in the race.

The Obamas raised the roof in Chicago on Tuesday, with the ex-first lady declaring that under Harris “hope is making a comeback.”

On Wednesday, Bill Clinton and television talk show host Oprah Winfrey were the warm-up acts for Harris’s running mate Tim Walz.