Trump holds rally in Pennsylvania on heels of Biden's official campaign launch Pa. was crucial to the president's 2016 victory and to his reelection hopes.

Speaking at his first Pennsylvania campaign rally since the 2018 midterms, President Donald Trump on Monday night ripped into former Vice President Joe Biden, called out FOX News for covering Democrats, touted the booming U.S. economy and pushed his supporters to come out for Tuesday’s special election.

Trump's first campaign rally in Pennsylvania comes just days after former Biden officially kicked off his presidential bid over the weekend, as both parties continue to make plays for the critical state.

"It’s no wonder that when Joe Biden announced that he was running for president -- by the way, we have thousands of people and I’m not even announcing today -- they said he had 600 people," Trump told his audience, some of whom laughed. "No, no, no, not very good. I’d say 150, and that was on an announcement."

Biden's campaign reported an expected crowd size of 2,000, and The New York Times cited security officials who said about 6,000 were there.

"And don't forget," Trump went on, "Biden deserted you. I guess he was born here, but he left you, folks. He left you for another state. I meant to say that."

For Trump, Pennsylvania holds weight: The state was crucial to the president's 2016 victory, and it again will be for his reelection hopes. The president pulled off a narrow victory in Pennsylvania in 2016, becoming the first Republican to win the state in nearly two decades.

The president landed in dramatic fashion on Air Force One -- to cheers from the crowd -- and then took the stage. Trump wasted no time touting the booming economy.

"When you've had the best employment numbers in history, when you have the best unemployment numbers in history, when you have the best economy we've ever had -- how the hell do you lose this election?" the president asked the raucous crowd in Montoursville, Pennsylvania.

Trump said the U.S. has the greatest economy anywhere in the world.

Trump also explained that one key reason he came back to Pennsylvania is because of Tuesday's "crucial" 12th Congressional District special election, where Republican state Rep. Fred Keller is looking to defeat Democrat Marc Friedenberg and replace Republican Tom Marino, who resigned shortly after the new Congress began earlier this year.

"You get out tomorrow. It's a little bit of a referendum," Trump urged his supporters Monday. "They'll say, 'President Trump came to Pennsylvania, and he went back home, a loser.'"

"I never want to be called a loser," Trump added.

Before the president took the stage, his eldest son, Donald Trump Jr., hyped up the hot crowd, many of whom had waited hours in line to get into the event. This marked the president's son's first appearance at a campaign rally since being called back to Congress for further testimony.

"They still can't let it go. God knows I gotta deal with that one myself despite 30 hours of testimony," Trump Jr. said. "I've done, you know, 25 to 30 hours of testimony in front of multiple committees, Senate, Congress. The Mueller report cites my congressional testimony. They cite my Senate testimony. Think about it. They cite my stupid Twitter account."

"They've looked at it all. And we're clear, but they still want to send you in there to go back and two years later, answer questions about something because Michael Cohen," Trump Jr. added.

Also ahead of the rally on Monday, the Trump campaign told ABC News that the president was excited to to tout the economy in the Keystone State, a message that will likely be embraced by voters as Pennsylvania is experiencing record low unemployment at 3.8% in April, the lowest level since 1976. The state's unemployment numbers are largely reflective of the declining unemployment rate throughout the country, frequently championed by the president at both the White House and on the campaign trail.

But despite a booming economy and his previous upset victory, Trump's campaign follows Republican defeats in the 2018 midterms. Democrats clenched key statewide races including the U.S. Senate and the gubernatorial race. A year prior, Democrat Conor Lamb claimed victory in a special House election by captivating voters in the heart of Trump territory, a district the president won in 2016.

As Republicans acknowledge warning signs ahead of the 2020 election, Democrats hope to capitalize on the momentum. Just a few hours away from where Trump will address his supporters in Montoursville, voters in Philadelphia received a rival pitch from a former vice president who hopes to challenge Trump.

"If the American people want a president to add to our division, to lead with a clenched fist, closed hand and a hard heart, to demonize the opponents and spew hatred -- they don't need me. They've got President Donald Trump," Joe Biden told a crowd during his campaign kickoff speech in his home state of Pennsylvania.

"I am running to offer our country -- Democrats, Republicans and independents -- a different path," Biden continued.

The former vice president also claimed the Trump administration "inherited an economy from Obama-Biden administration."

"That was given to him -- just like he inherited everything else in his life," Biden said.

Trump went on a Twitter spree earlier this month in an attempt to show he has support from firefighters after Biden netted a key endorsement from one of the nation's largest firefighter unions. The pair have exchanged sharp words, with Biden calling Trump the "Divider-in-Chief" and the president labeling Biden "sleepy creepy Joe" following allegations of sexual misconduct against the former vice president.

The state's Republican party released a statement in response to Biden's campaign announcement calling his campaign one that "seeks to paint over the failures of the Obama-Biden years and his record as U.S. senator while offering nothing but a continuation of those failed policies."