Vice President Kamala Harris is facing the most significant decision of her quarter-century political career – choosing a running mate to join her on the Democratic Party's national ticket.

And an announcement of her decision is expected in the coming hours – ahead of the first rally by Harris and her running mate Tuesday evening in Philadelphia.

It's the crucial moment in the most consequential stretch for Harris in the two weeks since she replaced President Biden at the top of the Democrats' 2024 ticket.

The vetting, screening and interviewing of running mates normally takes months. But these are far from normal times for the Democrats, and Harris is facing an extremely compressed timetable.

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Vice President Kamala Harris to announce her running mate on the Democrats' 2024 national ticket

Vice President Kamala Harris admires the crowd during a campaign rally, Tuesday, July 30, 2024, in Atlanta. (AP Photo/John Bazemore)

Harris stayed in the nation's capital this weekend, meeting in-person with Govs. Josh Shapiro of Pennsylvania and Tim Walz of Minnesota, and Sen. Mark Kelly of Arizona, three of the roughly half-dozen running mate contenders, Democratic sources confirmed to Fox News.

Among those also in contention, according to sources, are Govs. Andy Beshear of Kentucky and JB Pritzker of Illinois, and Transportation Secretary Pete Buttigieg.

Ahead of her meetings with the contenders, Harris was briefed by a vetting team led by former Attorney General Eric Holder.

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The rollout of the announcement is not known, but it's likely it could come through a video introduction, similar to how Biden announced Harris as his running mate four years ago. But the Harris campaign's plans could be upended on Monday or Tuesday by a media leak of the announcement.

It's been mostly smooth sailing for Harris since Biden's blockbuster announcement amid a rising chorus of calls from fellow Democrats to end his re-election bid following a disastrous debate performance in late June against former President Trump.

Over 10,000 at a Kamala Harris rally in Atlanta, Georgia

Vice President Kamala Harris speaks during a campaign rally, Tuesday, July 30, 2024, in Atlanta. (AP Photo/John Bazemore)

A party eager to keep Trump, the GOP presidential nominee, from returning to the White House quickly unified behind Harris. The vice president experienced a surge in contributions and more than doubled Trump in July fundraising, and volunteers flocked to Biden-turned-Harris campaign offices.

And the small but telling lead that Trump had built over Biden in the weeks following the late June debate instantly vanished, as the latest national and key battleground state polls indicated a margin-of-error race between Harris and the former president.

But the smooth sailing could potentially turn into choppier seas.

While Harris and her team have remained mostly quiet about the naming of a vice presidential nominee, allies of the contenders have been advocating on their behalf and interest groups within the party have been increasingly making their wishes known. 

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The announcement by Harris in the coming hours will likely disappoint some of those supporting candidates who weren't named as the running mate, and could exacerbate policy divisions between the moderate and progressive wings of the party that have been papered over the past two weeks.

Harris and her to-be-named running mate will team up on Tuesday at a rally in Philadelphia to kick off an ambitious and jam-packed swing state tour through Pennsylvania, Wisconsin, Michigan, North Carolina, Georgia, Arizona and Nevada, the seven battlegrounds that will likely determine the outcome of the presidential election.

The vice president drew over 10,000 at her first major rally since taking over for Biden at the top of the Democrats' ticket, last week at the Georgia State Convocation Center in Atlanta. 

It was the first time this cycle that the Democratic ticket drew a crowd comparable to the large audiences Trump has been regularly drawing for much of his more than year-and-a-half long campaign to return to the White House. And the size and energy of Harris' crowds during this week's swing state tour will be closely monitored.

Trump and his running mate – Sen. JD Vance of Ohio – held a rally at the same venue in Atlanta on Saturday, where the former president continued his relentless attacks and insults of Harris.

In social media posts earlier on Saturday and at the rally, Trump charged Harris had a "low IQ" and was "dumb," and accused her of lacking "mental capacity."

Donald Trump holds a rally in battleground Georgia

Former President Trump speaks at a campaign rally at Georgia State University in Atlanta, Saturday, Aug. 3, 2024. (AP Photo/John Bazemore)

The Harris campaign, firing back on Sunday morning, claimed that Trump was "weak… struggling… panicking… and Donald Trump is running scared."

Harris has yet to sit for a major interview since taking over for Biden, and the Trump campaign is turning up the criticism.

"Kamala Harris is too afraid to answer media questions and cannot lead us in these troubled times," Vance charged in a social media post on Monday.

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Vance plans to tail Harris as part of the Trump campaign's plan to bracket the vice president and her running mate on their initial swing state tour.

Sources in the senator's political orbit confirmed to Fox News that Vance will be in Philadelphia on Tuesday as the vice president kicks off her campaign swing. 

JD Vance to bracket Harris this week

Sen. JD Vance speaks at a campaign rally at Georgia State University in Atlanta, Saturday, Aug. 3, 2024. (AP Photo/John Bazemore)

Harris will start the week by formally landing the party's presidential nomination, as a virtual roll call run by the Democratic National Committee concludes at 6 p.m. ET. But there's no drama, as the vice president was the only candidate to qualify for the roll call.

The roll call kicked off on Thursday and DNC Chair Jaimie Harrison announced on Friday that Harris had clinched the nomination by winning the votes of a majority of delegates to the party's nominating convention, which gets underway in two weeks in Chicago.

While the past two weeks have been smoother than many expected, the Harris campaign is well aware there are still three months to go until the November election.

Battleground states director Dan Kanninen emphasized that "it is the task of the Harris campaign to turn the unprecedented energy behind the Vice President into action."

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.