Bidens on the trail: President and first lady campaign in the biggest of the battlegrounds

With a margin of error race between Vice President Kamala Harris and former President Trump and three weeks to go until Election Day, the two residents of the White House are heading to the biggest of the battlegrounds to campaign on behalf of Harris and down-ballot Democrats.

President Biden travels to his native state of Pennsylvania on Tuesday, as he serves as the main attraction at the Philadelphia Democratic City Committee's autumn fundraising dinner.

And first lady Jill Biden will be in suburban Philadelphia – as she headlines an afternoon event in Chester County and then speaks in the evening in Montgomery County, where she grew up.

The first lady is campaigning on behalf of Harris in the seven key swing states whose razor-thin margins decided her husband's 2020 victory over Trump and will likely determine if Harris or Trump succeed Biden in the White House.

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First lady Jill Biden speaks during a campaign stop Monday, Oct. 14, 2024, in Madison, Wisconsin. (AP Photo/Morry Gash)

Biden's latest campaign trail foray for fellow Democrats comes amid reports of a lack of coordination between political advisers to the president and the vice president.

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The appearances by both Bidens also come a day after the Democratic and Republican presidential nominees campaigned in Pennsylvania, with Harris holding two events in Erie, in the northwest corner of the state, and Trump in suburban Philadelphia, in the southeastern portion of the commonwealth.

Vice President Kamala Harris and President Biden arrive at a campaign event at the IBEW Local Union #5 hall in Pittsburgh, on Labor Day, Monday, Sept. 2, 2024. (AP Photo/Jacquelyn Martin)

It was the vice president's 10th visit to Pennsylvania since replacing Biden atop the Democrats' 2024 ticket in mid-July. Trump's also been a frequent visitor, with rallies in Scranton and Reading less than a week ago.

Pennsylvania, along with Michigan, Wisconsin, Georgia, North Carolina, Arizona and Nevada, had razor-thin margins that decided Biden's 2020 victory over Trump. And the seven states will likely determine whether Harris or Trump wins the 2024 presidential election.

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But with 19 electoral votes at stake, Pennsylvania's the biggest of the key battlegrounds. And while the campaigns and their allied super PACs are pouring resources into all seven states, more money has been spent running spots in Pennsylvania than any of the other battlegrounds, according to figures from AdImpact, a top national ad tracking firm.

Vice President Kamala Harris arrives to speak during a campaign rally at Erie Insurance Arena, in Erie, Pennsylvania, Monday, Oct. 14, 2024. (AP Photo/Jacquelyn Martin)

Pennsylvania, along with Michigan and Wisconsin, are the three Rust Belt states that make up the Democrats' so-called "Blue Wall."

The party reliably won all three states for a quarter-century before Trump narrowly captured them in the 2016 election to win the White House.

Four years later, in 2020, Biden carried all three states to put them back in the Democrats' column and defeated Trump.

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