Former vice president Joe Biden speaks during his first campaign event as a candidate for US President at Teamsters Local 249 in Pittsburgh, Pennsylvania, April 29, 2019.

The rally marked the 76-year-old Biden's first major public campaign event since his long-expected announcement last Thursday that he would run for president, becoming the 20th Democrat to join the race to unseat Trump in 2020. Despite his late arrival, the six-term former senator and two-term former vice president is widely considered a top contender in the crowded Democratic field.

"I came here because, quite frankly folks, if I'm going to beat Donald Trump in 2020, it's going to happen here," Biden told a packed Teamsters banquet hall in Pittsburgh.

Former Vice President Joe Biden on Monday kicked off his first campaign rally as a 2020 presidential candidate with a stump speech tailored toward America's workers — that also threw more than a few jabs at President Donald Trump .

Biden — speaking to a crowd filled with union members — steered his remarks heavily toward populist issues including corporate greed and income inequality.

"I make no apologies — I am a union man. Period," said Biden, who had received his first union endorsement earlier that morning.

"The country wasn't built by Wall Street bankers, CEOs and hedge fund managers," Biden told the crowd. "It was built by you. It was built by the great American middle class."

"We need to reward work in this country, not just wealth," Biden said.

As the roughly 20-minute speech went on, Biden dug in on Trump's character and his administration's policies.

"There was a $2 trillion tax cut last year. Did you feel it?" Biden asked the crowd, which responded with a loud "No!" in unison.

"Of course not!" he said, adding, "It's a one-way street these days."

Trump, said Biden, is "the only president who's decided not to represent the whole country."

Biden has taken aim directly at Trump from the very beginning of his candidacy last week. And Trump has not been shy about launching his own salvos. Ahead of Biden's Monday afternoon speech, Trump fired off a pair of tweets attacking the latest entrant to the presidential race, branding the political veteran with the derisive nickname "Sleepy Joe Biden."

@realDonaldTrump: The Media (Fake News) is pushing Sleepy Joe hard. Funny, I'm only here because of Biden & Obama. They didn't do the job and now you have Trump, who is getting it done - big time!

Trump also touted Pennsylvania's economic progress under his administration, saying Biden "obviously doesn't know" that the state "is having one of the best economic years in its history, with the lowest unemployment EVER." State officials reportedly said earlier this month that the Pennsylvania unemployment rate had fallen to 3.9% in March, its lowest point since 1976.

@realDonaldTrump: Sleepy Joe Biden is having his first rally in the Great State of Pennsylvania. He obviously doesn't know that Pennsylvania is having one of the best economic years in its history, with lowest unemployment EVER, a now thriving Steel Industry (that was dead) & great future!........

The early days of the former Delaware senator's campaign strategy appear to be aimed at shoring up his support in Pennsylvania, a swing state rich in electoral votes that former Secretary of State Hillary Clinton narrowly lost to Trump in the 2016 election.

Biden's first fundraising event as a candidate was held at the Philadelphia home of David Cohen, executive vice president of Comcast, the parent company of NBCUniversal. And he's scheduled to return to the city on May 18 to hold a rally that will lay out his campaign's vision for unifying a politically polarized country.

Biden has also showed a clear focus on gaining the support of labor unions. On the eve of his campaign announcement, Biden delivered some of his most fiery speeches to union crowds. And on Monday morning, he picked up the first major union endorsement of the presidential primary, gaining the blessing of the roughly 300,000-member International Association of Firefighters.

Other Democrats, eager to present themselves as champions of working Americans, have also taken steps to court the backing of labor unions by disavowing contributions from political action committees and calling for increased worker benefits and protections. Employees on the campaign of Sen. Bernie Sanders, I-Vt., who is running for president as a Democrat, have even formed their own union.