WASHINGTON, Aug 6, 2024 (BSS/AFP) - Kamala Harris was set to announce her running mate Tuesday before the pair head out on a five-day swing through America's hottest battleground states, just three months out from the presidential election.

The US vice president's campaign has come out of the blocks at a lightning pace since she replaced Joe Biden at the top of the Democratic ticket, smashing fundraising records and wiping out the leads built up by Republican rival Donald Trump.

Pennsylvania Governor Josh Shapiro, a Democratic rising star, is considered the favorite to join Harris as her vice-presidential pick, ahead of several other state governors, a US senator and Transportation Secretary Pete Buttigieg.

US media reported Monday that Harris had narrowed one of the most consequential choices of her political career to Shapiro and Minnesota Governor Tim Walz and would likely make her decision public in a video announcement.

Less than a day before their swing state journey, Harris was maintaining the suspense about her running mate, telling supporters in a text message Monday evening that "I have not made my decision yet."

Harris, 59, and her newly minted deputy will hold a rally Tuesday at Temple University in Philadelphia before hitting Wisconsin and Michigan on Wednesday, Arizona on Friday and Nevada on Saturday.

She was also intending to hold events in battlegrounds North Carolina on Thursday and Georgia on Friday, but local media outlets reported that a tropical storm battering southeastern states had forced their postponement. There was no response from the Harris campaign on a request for details.

Shapiro is enormously popular in Pennsylvania -- the largest of the six or seven swing states that have decided recent US elections -- and is seen as giving Harris a boost in what is considered must-win real estate for Democrats and Republicans alike.

The 51-year-old would be the country's first Jewish vice president, adding to the diversity of a ticket already boasting what would be the only woman ever sent to the Oval Office.

His support for Israel and handling of pro-Palestinian protests has sparked a leftist backlash, however, and Democrats are keen to ensure that their mid-August convention in Chicago isn't marred by progressive and anti-Israel activists.

- Hard fight -

Shapiro's backers have argued in any case that the criticism is rooted in anti-Semitism, and many analysts believe his moderate profile gains him more votes from the center than it loses on the progressive fringe.

Walz, a 60-year-old former National Guard officer who exudes folksy charm, would bring a rural Midwestern perspective to the ticket but is seen as being from the liberal wing of the party.

He has been making a name for himself as one of the Democrats' most effective communicators in recent weeks, with his criticism of Trump and running mate J.D. Vance as "weird" gaining enormous traction.

Other less likely contenders include Arizona Senator Mark Kelly, a former astronaut and war veteran; Kentucky Governor Andy Beshear, a longstanding friend of Harris; and Illinois Governor J.B. Pritzker.

Harris threw her hat in the ring and began her search for a running mate after 81-year-old Biden exited the race on July 21.

He had been facing mounting concerns over his low popularity ratings and advanced years, and Trump was surging after surviving an assassination attempt and presiding over a united party at the Republican National Convention in Milwaukee.

Multiple recent polls have shown Harris's rise continuing unabated ever since, with a Morning Consult survey notably placing her four points ahead of Trump nationally, 48 to 44 percent.

But a new CBS News poll found Harris's popularity among Black voters some way behind Biden's score as he defeated Trump in 2020, prompting some senior Democrats to caution against complacency.

"She has a lot of momentum, but if you do look at the polling, this is still a really tight race," Barack Obama's one-time strategist David Axelrod told political outlet The Hill. "This is going to be a hard fight for either side."