MONTOURSVILLE, Pa. (AP) — President Donald Trump voiced confidence Monday in his ability to win Pennsylvania in 2020 and took a new swipe at one of his leading Democratic rivals, telling rallygoers in the state that native son Joe Biden had abandoned them by representing Delaware in the Senate.

The president's visit to Pennsylvania, intended to boost Republican congressional candidate Fred Keller's prospects over Democrat Marc Friedenberg in a Tuesday special election for an open seat, had as much to do with helping his own chance for reelection as it did with pushing Keller over the finish line.

"We've got to win tomorrow, Fred," Trump told a cheering rally crowd at a private hangar at Williamsport Regional Airport. He later added:

Trump's visit to the key battleground state also came two days after Biden held a campaign rally in Philadelphia, and the former vice president wasn't far from Trump's mind.

The president accused Biden, who was born in Pennsylvania and has long ties there, of deserting his state by representing Delaware in the Senate. Biden moved to neighboring Delaware with his family as a boy.

"He left you for another state, and he didn't take care of you," Trump said.

He also referred to the former vice president by the nickname he had coined for him: "Sleepy Joe."

"Sleepy Joe said that he's running to, quote, 'save the world,'" Trump said. "Well, he was. He was going to save every country but ours."

Biden said Monday in Nashville, Tennessee, that he was running on a pledge to restore the soul of the country. He has frequently talked on the campaign trail about the president's divisive rhetoric and said another four years of Trump would "fundamentally change the character of this nation."

Trump, who spoke in the open air with Air Force One behind him, highlighted the economy's performance under his leadership and suggested those numbers would make him virtually unbeatable.

"Politics is a crazy world, but when you have the best employment numbers in history, when you have the best unemployment numbers in history ... I don't know, how the hell do you lose this election, right?" Trump said. The current unemployment rate of 3.6% is actually the lowest since 1969, when it stood at 3.5%. Unemployment was even lower than that in the early 1950s, and much lower, under 2%, during three years of World War II.

Keller himself offered a rousing endorsement of Trump, saying he wants to go to Congress to be a vote for Trump. Keller told Trump the people of this region of Pennsylvania "have been behind you since Day One, and, Mr. President, our support for you is as strong today as it ever was."

"In 2016, Pennsylvania put Donald Trump over the top. And in 2020, we're going to do it again," Keller said.

Trump uses his campaign rallies to disparage various Democratic candidates for president, but he has been heavily focused on Biden, suggesting he may be worried about the possibility of facing off next year against the longtime politician.

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