President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Monday blasted union leaders after former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE received the endorsement of a major firefighters labor group.

“I’ll never get the support of Dues Crazy union leadership, those people who rip-off their membership with ridiculously high dues, medical and other expenses while being paid a fortune. But the members love Trump,” the president said.

I’ll never get the support of Dues Crazy union leadership, those people who rip-off their membership with ridiculously high dues, medical and other expenses while being paid a fortune. But the members love Trump. They look at our record economy, tax & reg cuts, military etc. WIN! — Donald J. Trump (@realDonaldTrump) April 29, 2019

Trump, who has long claimed support of rank-and-file union members, added that “they look at our record economy, tax & reg cuts, military etc.” and see a “WIN!”

ADVERTISEMENT

The president’s latest attack came hours after the International Association of Fire Fighters announced it would endorse Biden's 2020 Democratic presidential bid after staying out of the 2016 election, declining to endorse Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE or Trump.

While it was widely expected, the endorsement gave Biden a boost as he got set to hit the campaign trail for the first time on Monday with a rally in Pittsburgh.

People close to Trump believe Biden could be the president’s most formidable general election opponent, since he could earn support from white, working-class voters in states Trump won in 2016, including Pennsylvania, Michigan and Wisconsin.