First and potentially only presidential debate between Harris and Trump being held in crucial battleground

PHILADELPHIA — It's fitting that Tuesday night's debate between Vice President Harris and former President Trump is being held in the key general election battleground state of Pennsylvania.

Harris and Trump face off at 9 p.m. ET at the National Constitution Center in Philadelphia, the largest city in the Keystone State. The debate is the first and potentially the only showdown between Harris and Trump.

Both candidates have repeatedly made stops this summer in Pennsylvania, which was one of seven key swing states that decided the outcome of the 2020 election between Trump and President Biden. And Pennsylvania, along with Michigan, Wisconsin, Georgia, North Carolina, Arizona and Nevada, will likely determine who wins the White House in November.

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While the campaigns and their allied super PACs are pouring resources into all seven states, more money has been spent to run spots in Pennsylvania than any of the other battlegrounds. And both sides have dished out more dollars to reserve airtime going forward in the Keystone State than any of the other battlegrounds in the final eight weeks leading up to Election Day on Nov. 5, according to figures from AdImpact, a top national ad tracking firm.

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"It's the one state that it's hard to see someone losing and then still winning the presidential race," Mark Harris, Pittsburgh-based longtime Republican national strategist and ad maker, told Fox News Digital. "It's clearly ground zero."

Harris, a veteran of multiple GOP presidential campaigns said, "You can see that in media reservations and in the candidates' travel schedules. Clearly, the Trump campaign and the Harris camp believe this is a must-win situation."

Mike Butler, a Pittsburgh-based Democrat consultant, told Fox News Digital that when it comes to the White House race, "I don't think any other state quite swings the needle as much as Pennsylvania."

It is not just the top of the ticket campaigning in Pennsylvania. Minnesota Gov. Tim Walz, the Democrats' vice presidential nominee, and Sen. JD Vance of Ohio, Trump's running mate, have made numerous stops in the state.

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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 by razor-thin margins to put them back in the Democrats' column and defeated Trump.

Fast-forward to the present day, and Pennsylvania remains a jump ball as the latest public opinion surveys in the state indicate a margin-of-error race between Harris and Trump. 

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"It's going to be a fight to the finish. I think Trump has some advantages," Mark Harris said. "But its definitely going to be a very tight race."

Butler noted that Pennsylvania's had razor-thin margins in the past two presidential elections.

"Trump's numbers are pretty solidly baked in. I can't see him faring any worse than he did the last two times, which means it's going to be a very competitive state," he said.

This isn't the first time a presidential debate has been held at the National Constitution Center, which opened 21 years ago and is located on the north end of Independence Mall in Philadelphia's Old City neighborhood.

The venue hosted a 2008 Democrat presidential primary debate.

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