WASHINGTON, Aug 15, 2024 (BSS/AFP) - Joe Biden and Kamala Harris on Thursday will make their first joint trip since the US president dropped out of the 2024 election, delivering a major economic announcement aimed at boosting Harris's White House hopes.

Biden, 81, and Harris, 59, will put on a show of unity at an event in Maryland, near Washington, less than three weeks after their seismic switch-up at the top of the Democratic Party ticket to face Donald Trump.

Biden indicated on Wednesday that the announcement would involve his core policy of reducing drug prices, while the White House said they would unveil steps to "lower costs for the American people."

It comes a day before Vice President Harris is due to finally set out her own economic agenda on Friday, and ahead of her star turn at the Democratic National Convention next week.

Trump will meanwhile try to steal their thunder as he holds a press conference shortly after the event.

The Republican former president has so far struggled to deal with the upended White House race that has seen Harris wipe out his lead in the polls and draw huge crowds to her rallies.

Yet things are delicate for the Democrats too, with Biden still coming to terms with his decision to step aside from the election following a disastrous debate against Trump, even as Harris rides a wave of enthusiasm.

Harris is also trying to keep some distance from Biden's policies without trying to undermine the man who is still commander-in-chief for another five months.

- 'Fine line' -

The news outlet Axios reported on Wednesday that Harris wants to "break with Biden on issues on which he's unpopular," with rising prices being top of the list.

The issue of inflation has dogged Biden's presidency, with many voters rating him poorly on the economy despite otherwise good numbers for jobs and growth.

Conversely, more Americans now trust the vice president to handle the economy than Trump, at 42 percent to 41 percent, according to a Financial Times and University of Michigan poll.

Before she took the reins, Biden was at 35 percent, while Trump's number is unchanged.

In the battleground state of North Carolina, Harris will make her first proper policy speech on Friday, reportedly focusing on lowering the price of groceries for hard-hit Americans.

But while Harris is trying to set out her own policy agenda, she will be careful not to bad-mouth the policies of an administration in which she is a key member.

"It's a fine line to walk for her," Casey Burgat of George Washington University told AFP.

For his part, Biden has offered his full backing to Harris and said that it was time to "pass the torch."

The only other time they have appeared together since Biden stepped back was at an air force base to welcome back US journalist Evan Gershkovich and other prisoners freed in a swap with Russia on August 1.

Since Biden dropped out, Trump has accused Harris of mounting a "coup" against the president, and often seems to spend more time talking about his former opponent than his current rival.

His press conference on Thursday at his New Jersey golf course will be the latest in a series of attempts at wresting back attention from Harris.