WASHINGTON (AP) — Vice President Kamala Harris will introduce her new running mate at a rally Tuesday evening in Philadelphia — but with the event mere hours away, her choice remains a mystery.

In recent days, she has zeroed in on a trio of potential finalists: Pennsylvania Gov. Josh Shapiro, Arizona Sen. Mark Kelly and Minnesota Gov. Tim Walz, but decisions beyond that aren't yet publicly known.

Harris' campaign planned to make the announcement via video message before the rally, though the exact timing remained unclear, according to a person involved in the planning who spoke on the condition of anonymity to detail discussions occurring behind closed doors.

Doing so would be similar to how then-candidate Joe Biden revealed Harris as his vice presidential choice during the pandemic-marred presidential race of 2020.

It will mark yet another major milestone in the barely two weeks since the vice president moved to take over the top of the Democratic ticket heading into November's election. She has been scrambling to build out a campaign since then, and to breathe new life into the Democratic race against Republican Donald Trump.

Harris, second gentleman Doug Emhoff and her No. 2 pick are set to appear together for an evening rally in Philadelphia, recalling a joint 2020 appearance by Biden and Harris in Wilmington, Delaware. Likewise, in 2016, newly selected running mate Sen. Tim Kaine of Virginia appeared with Hillary Clinton in Miami.

After Tuesday's day trip to Pennsylvania, Harris and her running mate will spend the next five days flying thousands of miles around the country, touring critical battleground states. They'll visit Eau Claire, Wisconsin, and Detroit on Wednesday. But a planned stop in Savannah, Georgia, was postponed due to Tropical Storm Debby 's effects, and rain associated with it could also upend a scheduled stop in Durham, North Carolina.

Later in the week, Harris and her No. 2 will head to Phoenix and Las Vegas.

That the schedule was set before her running mate was identified recalls a cliffhanger-like scenario that Trump created by holding off on making his choice of vice presidential hopeful, Ohio Sen. JD Vance, until last month's Republican National Convention was under way in Milwaukee.

Vance, meanwhile, is aiming to detract from the debut of Harris' pick on Tuesday. He planned to arrive in Philadelphia ahead of the Democratic ticket and offer his own speech at midday, as counterprogramming.

The senator then announced he'd shadow Harris and her running mate with his own events in Wisconsin, Michigan and North Carolina. It was unclear how the weather might affect his southern swing.

In announcing Vance's travels, the Trump campaign laid the blame for a litany of woes on Harris and Democratic policies, saying that "prices are excruciatingly high, cost of living has soared, illegal immigrants are pouring into our country, and crime is running rampant. The stock market is crashing because of weak, failed, and dangerously liberal Kamala Harris' policies."

Harris' campaign, for its part, welcomed the overlapping destinations.

"We appreciate JD Vance providing voters in battleground states exactly the split-screen that defines the choice this November," said Harris campaign spokesman Charles Lutvak.

The vice president's campaign says it has invited faith leaders, union members and state and local elected officials to participate in the upcoming events. Harris and her running mate plan to rally in a variety of venues, from large arenas to college campuses. The trip will also allow them to see voters in smaller settings like union halls, family owned restaurants and campaign field offices.

At a fundraiser in Minneapolis on Monday night, Walz said Trump has stolen America's joy and was limiting freedoms.

"It wasn't a slur to call these guys weird," Walz said of the label he has applied to the GOP ticket in recent days. "It was an observation."

It's a characterization that has since taken off in Democratic circles.

If Harris opts for Shapiro, who hails from the Philadelphia suburbs, Tuesday's event with her there would be a homecoming of sorts.

Consideration of Shapiro has drawn criticism from some Arab Americans and activist groups wary of his professed solidarity with Israel in its drive to eliminate Hamas during the war in Gaza. But Shapiro enjoys strong approval ratings in Pennsylvania — one of the Democrats' crucial "blue wall" states along with Michigan and Wisconsin — that Harris will be looking to cement ahead of November.

On a "Progressives for Harris" organizing call Monday night that organizers said drew tens of thousands of participants, speakers repeatedly derided Israeli Prime Minister Benjamin Netanyahu as an "authoritarian" who was needlessly targeting and killing civilians in Gaza.

Some delegates to the Democratic National Convention who supported " uncommitted " rather than Biden because of his administration's backing of Israel, also suggested that they weren't yet ready to support Harris until they knew more about her policies, including if she'll work more diligently toward a ceasefire in the Gaza fighting.

But those on the call refrained from criticizing Harris' potential running mates, instead focusing on Trump.

"Trump and JD Vance are promising more tax cuts for the mega-millionaires and billionaires," said Massachusetts Sen. Elizabeth Warren. "This election is our chance to tax the rich and make the wealthy pay their fair share."

As for Kelly, some congressional Democrats have promoted the former astronaut whose state has more than 370 miles (600 kilometers) of border with Mexico. They say his selection could help defuse Trump's arguments that the Biden-Harris administration's immigration policies are too relaxed — though some union leaders have suggested the senator isn't as friendly to organized labor as they'd like.