President Trump focused on the economy at a fiery rally at the Energy Aviation Hangar in Montoursville, Pennsylvania Monday evening, just two days after 2020 Democrat presidential frontrunner Joe Biden held his own campaign rally in nearby Philadelphia.

And Trump caustically reminded the hometown crowd that the Biden -- who was born in Scranton, Pa. -- quickly took his political career to neighboring Delaware.

"And don't forget: Biden deserted you," Trump said as the rally wrapped up. "He's not from Pennsylvania. I guess he was born here, but he left you folks. He left you for another state. Remember that, please. I meant to say that. This guy talks about, 'Oh, I know Scranton.' Well, I know the places better. He left you for another state, and he didn't take care of you, because he didn't take care of your jobs. He let other countries come in and rip off America. That doesn't happen anymore."

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The pivotal battleground state could determine the next occupant of the White House. But on Monday, the president was largely in town to campaign on behalf of Republican Fred Keller, who faces Democrat Marc Friedenberg in Tuesday's special election to fill the U.S. House seat formerly held by Republican Rep. Tom Marino, who resigned in January.

Trump called the vote "crucial" and "a little bit of a referendum" on his presidency, and reminded the audience that pollsters had predicted he would lose the state in 2016. Keller, who walked off Air Force One with Trump, spoke briefly at the rally, saying he appreciated Trump showing his "support for the hardworking people of Pennsylvania's 12th Congressional District."

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Voters in the heavily GOP district overwhelmingly backed Trump over Hillary Clinton in the 2016 presidential election, helping Trump narrowly win the state overall.

Monday's rally reflected the district's enthusiasm. At one point, Trump invited a man up to the stage wearing a "MAGA hat" and a jacket decked out in a wall pattern, as the crowd chanted, "Build the wall!"

And a deafening chorus of "Lock her up" broke out the first time Trump mentioned Clinton.

President Donald Trump boards Air Force One for a trip to a Montoursville, Pa., for a campaign rally, Monday, May 20, 2019, at Andrews Air Force Base, Md. (AP Photo/Evan Vucci)

The heat was turned up at the rally in more ways than one: At least three individuals apparently fainted during Trump's remarks, as temperatures hit nearly 80 degrees.

"I don't know who got those lights, but they're very bright," Trump said, as audience members called for the lights to be turned down. "A real genius got those lights."

The U.S. economy saw 263,000 jobs created just last month, Trump noted, "far exceeding any expectations." With historically low unemployment rates and positive economic indicators across the board, including in Pennsylvania, Trump asked, "How the hell do you lose this election?"

"I think next time we're just going to have to get a bigger hanger," Trump said at the start of the rally, as the oversized crowd broke out into a sustained chant of "four more years."

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Large crowds had assembled early Monday at Williamsport Regional Airport in Montoursville, as supporters eagerly awaited the first presidential visit to Lycoming County in nearly two decades.

"Get out and vote -- can't take a chance," Trump said. "You joined our movement because you rejected the failures and betrayals of the past. ... You reclaimed your destiny, you defended your dignity, and you took back your country."

As Trump derided what he called the "treason" of the secret FBI investigations into his campaign that presented "artificial obstacles" to his candidacy, and chants of "Lock them up" rang out, Trump remarked, "Well, we have a great new attorney general who's going to give it a fair look."

"You've always been loyal to this nation. Now, you finally have a president who is loyal to you," Trump concluded. "Your dreams are my dreams. Your hopes are my hopes. And your future is what I'm fighting for, each and every day."

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Fox News' Brooke Singman and The Associated Press contributed to this report.