Kamala Harris is expected to take on companies unfairly jacking up prices as she sets out her economic agenda Friday in her first major policy announcement as the Democratic Party's presidential nominee.

The vice president, who replaced President Joe Biden atop the ticket last month, has been carried by surging enthusiasm, bolstered by new government figures this week showing inflation cooling.

More Americans now trust Harris to handle the economy than her Republican rival Donald Trump, according to a new University of Michigan poll, the first time in this election cycle that the former president has been behind on the issue.

But with the Democratic National Convention just days away, the 59-year-old vice president has been under increasing pressure to tell voters exactly what she stands for.

And while she has previewed a handful of policies, she has yet to settle on a concrete plan for governing, instead framing the sprint to the November 5 election in broad terms as a "fight for the future."

"Elections aren't just about winning. They're about accumulating political capital for a particular agenda, which Ms. Harris can't do unless she articulates one," the conservative Wall Street Journal said in an editorial.

Harris's first economic proposal -- to not tax tips -- perplexed some Democrats, who mocked the proposal as a "ploy" for votes after Trump first floated something similar.

She was on firmer ground on Thursday as she touted a likely vote-winning cut in medication costs for seniors and took part in her first joint public event with Biden since she replaced him amid concerns over his mental acuity.

In her widely anticipated speech in Raleigh, North Carolina on Friday, Harris is expected to call on Congress to pass the first federal ban on so-called "price-gouging" that will come with penalties on food companies that unfairly increase prices.

Personal attacks

Harris will also draw a contrast with Trump's economic vision, US media reported, arguing that his plan for tariffs of up to 20 percent on imports will drive up costs for food and other everyday items.

Some strategists have been telling Harris to keep things vague -- avoiding potentially divisive granular policy detail -- as long as the wave of enthusiasm over her candidacy shows no signs of breaking.

Others have advised her to put some distance between herself and Biden, who has struggled in his approval ratings on the economy, although their joint appearance Thursday suggested they remain close.

Harris has adopted much of Biden's economic agenda, promising to eradicate "junk fees" while bringing down prescription drug prices and housing costs -- and keeping the president's no-tax-hikes pledge for those making under $400,000.

On Friday, she will "launch an urgent and comprehensive four-year plan to lower housing costs for working families and end America's housing shortage", campaign officials said.

Harris will call for the construction of three million new housing units over the course of her first term, introduce increased tax incentives to builders of starter homes and rental housing, and take on corporate landlords who are jacking up rents.

Trump has been seething since Biden bowed out of the presidential race and passed the torch to Harris on July 21, and Republicans have been begging the former president to focus on policy and quit his personal attacks on his new opponent.

But Trump has been unable to stay on message, griping about Harris's crowd sizes, attacking her mixed race heritage and calling the former California attorney general stupid.

In a rambling North Carolina speech Wednesday meant to focus on his own economic message, Trump devoted much of his attention to personal insults and even said he was "not sure" that the economy is the "most important subject" in the election.