WASHINGTON (AP) — With fire fighters chanting “Run Joe, run,” former Vice President Joe Biden on Tuesday teased out themes of a possible presidential candidacy, criticizing President Donald Trump’s leadership while questioning Republicans’ commitment to middle class America.

Biden, a Democrat, has not announced a presidential bid. But he asked members of the International Fire Fighters Association gathered in Washington to save their energy, because “I may need it in a few weeks.”

Then he cautioned them to “Be careful what you wish for.”

During a speech that lasted about 30 minutes, Biden repeatedly tore into Republicans — and Trump — as supporting policies that favor the wealthy to the detriment of the middle and working classes.

Biden questioned those who oppose collective bargaining rights, saying: “Who the hell are these guys?”

And he singled out the Republican-championed tax cut signed into law by Trump, arguing that Republicans want to pay for it with devastating cuts to the social safety net.

“I’ll never understand people who fight you on the basics, like safety, fair play health care,” Biden said.

He expanded his critique of Trump to broader themes about the country’s founding principles.

“We can’t be divided by, race religion, by tribe. We’re defined by those enduring principles in the Constitution, even though we don’t necessarily all know them. In America everybody gets a shot,” Biden said. He added: “That’s what I don’t think this current president understands at all.”

He also questioned Trump’s “America First” foreign policy.

“Who fills the vacuum if we continue to walk way and walk off the world stage?” he asked. “This is America, so it’s time to get up remember who the hell we are.”

By: Brian Slodysko, Associated Press