U.S. Vice President and Democratic presidential candidate Kamala Harris. / Reuters/Elizabeth Frantz

Some 14,000 ecstatic voters packed a Philadelphia arena on Aug. 6 to see their favorite candidate. The next day in Eau Claire, Wisconsin, a line of thousands bound for a political rally there stretched more than half a mile.

Such impressive numbers have been common at Donald Trump campaign events. But these boisterous, jumbo crowds were not for him; they had come to see US Vice President Kamala Harris, his White House rival who has skyrocketed towards Democratic flagbearer status.

"Everybody is really hyped," 46-year-old Kina Johnson, who works at automaker Stellantis, told AFP on Aug. 7 at an airfield in Detroit, Michigan where a huge rally crowd -- packed into a hangar and spilling onto the tarmac -- awaited Harris and her freshly minted running mate Tim Walz.

"I think they're going to be bigger (and) more positive," Johnson said of the Democrats' campaign rallies. "It's a good thing for women actually right now, this is making history."

Walz, the governor of Minnesota, appeared stunned by the sea of supporters in Michigan, a critical election battleground. Campaign staff put it at 15,000 people, and Walz proclaimed it "the largest rally of the campaign."

The sight of so many Americans attending a Democratic political event was more common during the Barack Obama era, when a charismatic young Black candidate broke barriers to become president.

It has been beyond rare in the dozen years since Obama, and Trump -- acutely mindful of the numbers game and insisting large crowds correlate to broad support -- relentlessly plays up the disparity on the campaign trail.

But that advantage, less than three months before an immensely consequential presidential election, has evaporated as Harris and Walz send a jolt of enthusiasm through the Democratic Party base.

That has translated into attendance numbers off the charts compared with the smaller, quieter crowds that President Joe Biden has drawn this election cycle, or four years ago when he won during the coronavirus pandemic that squelched large gatherings.

He and 2016 nominee Hillary Clinton could never compete with Trump's sprawling, chaotic road show, which featured overflow crowds, salty-language merchandise, and fervent supporters camping out overnight to ensure front-row seats.

But with Biden bowing out of this year's race, Trump's new rival quickly showed she is more than capable of challenging the brash Republican in the rally size game -- and clearly it has gotten under Trump's skin.

Harris filled a 10,000-capacity arena last weekend in Atlanta, Georgia, her first major rally since becoming the Democratic presumptive nominee. She enlisted two hip-hop stars to excite the crowd.

Four days later Trump rallied at the same venue, with a similar-size crowd, and immediately attacked "Crazy Kamala" and her "lots of empty seats."

"I don't need entertainers," Trump told the crowd. "I fill the stadium because I'm making America great again. That's our entertainment."

Trump didn't stop there. Clearly agitated, he accused the hosts of preventing 1,000 more guests from getting in.

- Trump advantage 'disappears' -

"It has been a point of pride among Trump's supporters that his rallies have attracted much larger crowds than did Biden in 2020 or Clinton in 2016," Barry Burden, professor of politics at the University of Wisconsin-Madison, told AFP.

Such manifest support fueled Trump voters' suspicions about the validity of the 2020 election results.

"Now that Harris is speaking to large crowds that rival or exceed Trump's, this rationale for believing Trump is the advantaged candidate disappears," Burden added.

Trump has milked such advantages from the start of his political career. In 2015 he packed an Alabama football stadium with a reported 30,000 people.

As president, he was thrilled to use Air Force One as the ultimate campaign prop, roaring into his rallies and deplaning as awestruck supporters snapped cell-phone pictures.

But on Aug. 7 Harris took a page straight from Trump's campaign playbook, by rolling up to her own Detroit rally aboard Air Force Two, the vice-presidential jet.

Trump had sought to corner the patriotic imagery market, and his appearances on the campaign trail are still met with chants of "USA! USA!"

The same refrain was also heard, however, at Harris's raucous Philadelphia rally, something that rarely occurred at more subdued Biden events.