(AFP) - Kamala Harris was closing in on her vice-presidential pick Monday, with an announcement expected within 24 hours as she scrambles to introduce herself to the American public with a tour of battleground states just three months out from the election.

All paths to the White House run through a handful of swing states, and Harris will kick off her five-day run Tuesday in the largest -- Pennsylvania -- as she builds momentum for her showdown with Republican Donald Trump on November 5.

"This election is a fight for our country, our future, and our most fundamental freedoms and rights," she posted on X on Monday.

"We believe in the promise of America -- and we're in this fight because we know what's at stake."

Fresh from winning enough delegate votes to secure the Democratic nomination, the country's first female, Black and South Asian vice president heads into the national convention in Chicago in two weeks in total control of her party.

The 59-year-old former prosecutor has obliterated fundraising records, attracted huge crowds and dominated social media on her way to erasing the polling leads Trump had built before President Joe Biden quit the race.

Next on the agenda is a vice presidential pick, with an announcement expected on Tuesday, before her evening rally alongside the mystery nominee in Philadelphia, Pennsylvania's largest city.

The Keystone State is the most prized real estate among the closely fought battlegrounds that decide the Electoral College system.

It is part of the "blue wall" that carried Biden to the White House in 2020, alongside Michigan and Wisconsin -- two states where Harris is due to woo crowds on Wednesday.

Pennsylvania is governed by 51-year-old Democrat Josh Shapiro, a frontrunner in the so-called "veepstakes" shortlist that also includes fellow state governors Tim Walz and Andy Beshear, as well as Arizona Senator Mark Kelly and US transportation secretary Pete Buttigieg.

- 'Freedom' -

Later in the week, Harris will tour the more racially diverse Sun Belt and southern states of Arizona, Nevada, Georgia and North Carolina, as she seeks to shore up the Black and Hispanic vote that had been peeling away from the Democrats.

Just a month ago, Trump was in cruise control, having opened a significant lead in swing state polling after a dismal debate performance by Biden, with the Republican tycoon keeping the country in suspense over his own vice-presidential pick.

Trump's White House bid was upended on July 21 when 81-year-old Biden, facing growing concerns about his age and lagging polling numbers, exited the race and backed Harris.

Energetic and two decades younger than 78-year-old Trump, the vice president has made a fast start, raising $310 million in July, according to her campaign -- more than double Trump's haul.

While Biden made high-minded appeals for a return to civility and the preservation of democracy, Harris has focused on the future, making voters' hard-fought "freedom" the touchstone of her campaign.

She and her allies have also been more aggressive than the Biden camp -- mocking Trump for reneging on his commitment to a September 10 debate and characterizing the convicted felon as an elderly crook and "weird."

While she has disavowed some of the leftist positions she took during her ill-fated 2020 primary campaign, Harris hasn't given a wide-ranging interview since jumping into the race, and rally-goers will look for more detail on her plans for the country.

Meanwhile, Trump and his Republicans have struggled to adapt to their new adversary and hone their attacks against Harris -- at first messaging that she was dangerously liberal on immigration and crime, before suggesting she was lying about being Black.

© Agence France-Presse