U.S. President Donald Trump sits in the cab of a truck as he welcomes members of American Trucking Associations to the White House March 23, 2017 in Washington, DC. President Trump hosted truckers and CEOs for a listening session on healthcare. Alex Wong | Getty Images

President Donald Trump on Monday unleashed a series of tweets criticizing leaders of major labor unions and former Vice President Joe Biden, who launched his 2020 presidential campaign last week. Biden was scheduled to speak to the Teamsters union Monday in Pennsylvania, a state Trump won in 2016, but where Biden was born and raised. "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," Trump tweeted at around 10:30 AM. "But the members love Trump. They look at our record economy, tax & reg cuts, military etc. WIN!"

"Sleepy Joe Biden is having his first rally in the Great State of Pennsylvania," Trump wrote 10 minutes later. "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!........" Four minutes after his tweet about Pennsylvania, Trump wrote, "The Dues Sucking firefighters leadership will always support Democrats, even though the membership wants me. Some things never change!" TRUMP TWEET In response to Trump's attack, Biden tweeted, "I'm sick of this President badmouthing unions. Labor built the middle class in this country. Minimum wage, overtime pay, the 40-hour week: they exist for all of us because unions fought for those rights. We need a President who honors them and their work." BIDEN TWEET Earlier in the day Monday, the International Association of Fire Fighters announced that it would endorse Biden in 2020. In a video posted on YouTube, IAFF's general president, Harold Schaitberger, said Biden, "will be a champion for the public's safety in America, fighting for policies and legislation that improve the lives and livelihoods of not just firefighters, but all who work for a living." Trump made traditionally union-backed positions, like trade protections and raising tariffs, into pillars of his successful 2016 presidential campaign. And support from Democratic-leaning union households in states like Pennsylvania, Ohio, Michigan and Wisconsin no doubt helped Trump win these states by the slim margins he did.