PITTSBURGH — Former Vice President Joe Biden made his first official appearance as a 2020 presidential candidate Monday, taking on President Donald Trump at a campaign rally and imploring Americans to rebuild the middle class.

"Donald Trump is the only president who's decided not to represent the whole country," Biden said at a Teamsters hall. "We need a president who represents all Americans."

"We have to choose hope over fear, unity over division and maybe, most importantly, truth over lies," Biden added.

The former vice president made no reference to the other Democratic candidates and stuck largely to familiar issues.

Advisers have said his campaign will deal with three major themes — restoring the soul of nation, rebuilding the backbone of America and unifying the polarized country — offering an economic argument in moral and sometimes populist terms.

"The country wasn't built by Wall Street bankers, CEOs and hedge fund managers. It was built by you. It was built by the great American middle class," Biden said. "The stock market is roaring, but you don't feel it. There was a $2 trillion tax cut, did you feel it? Did you get anything from it? No! Of course not."

Taking a page from the book of Sen. Sherrod Brown, D-Ohio, Biden declared, “The dignity of work is my measure of success." And he said unions were a key part of that: "I make no apologies — I am a union man. Period."

Biden said the "basic bargain" between classes had broken down.

Now, he said, instead of workers and management benefiting in good times and suffering together in bad ones, it's a "one-way street" where management takes too much of the upside and workers bear most of the brunt of the downside.

"The major moral obligation of our time is to restore, rebuild, and respect the backbone of America — the middle class," he said.

The former vice president also staked a position on a key policy issue, saying he supports a public option that would allow all Americans buy into Medicare. That's where most of the Democratic presidential field has landed on health care, while Sen. Bernie Sanders, I-Vt., continues to press for a full-blown single-payer system that would virtually eliminate the private health insurance industry.

Biden also said it is "well past time" to raise the minimum wage to $15 an hour.

He was introduced by his wife, Jill, along with Harold Schaitberger, the president of the International Association of Fire Fighters, which endorsed Biden Monday and argued he had the best chance of beating Trump.

Schaitberger said there is "nothing phony or artificial about Joe Biden" and that "we need Joe more than Joe needs to be president." He also took a shot at Hillary Clinton.

Biden "connects with those workers who don’t believe the last Democratic nominee listened to them or cared about them," Schaitberger said, adding that he appeals to people who "feel their votes were being taken for granted."

Schaitberger also warned Democrats against nominating someone "who has high minded ideals but can't win."

"Let me shoot straight with you, and this may not be popular in parts of the Democratic Party — we can't have a nominee that's too far left, it's just that simple,” he said.

Mike Memoli reported from Pittsburgh, Alex Seitz-Wald reported from Washington.