PITTSBURGH — Sen. Bernie Sanders on Sunday accused President Donald Trump of betraying the working people who put him in office and challenged him to deny federal contracts to General Motors until the company reopens shuttered plants.

"The biggest lie was that he was going to stand up for working families and take on the establishment," the Democratic presidential contender told a Pittsburgh rally in his first visit of 2019 to the critical battleground state of Pennsylvania. "That was a monstrous lie."

Earlier in Lordstown, Ohio, and again in Pittsburgh, Sanders pressed Trump to put action behind his words on GM plant closings. Trump has assailed the company for shutting its small-car factory in Lordstown, in a politically important state, complaining about the company's leadership and a local union leader while seldom mentioning the other U.S. factories that GM plans to close.

That's not enough, Sanders said.

His message to GM and other multinationals: "If you want a federal contract paid for by taxpayers, treat your workers with respect and dignity. No more paying your workers inadequate wages while you provide CEO's with multimillion-dollar parachutes, no more taking away health care benefits, no more denying workers the right to form a union.

"And if you are not a good and responsible corporate citizen, do not think that you will get federal contracts."

Several union organizers spoke before Sanders at the Pittsburgh rally, part of Sanders' four-day, five-state swing through states that are part of the Democratic strategy to rebuild the "blue wall" in 2020. Sanders attracted an estimated 4,500 on the warm, breezy late afternoon to a grassy plaza near the campuses of Carnegie Mellon University and the University of Pittsburgh.

Democrats are putting a heavy emphasis on winning back three states Trump narrowly captured in 2016: Wisconsin, Michigan and Pennsylvania. Dubbed the "blue wall" before they unexpectedly tipped to Trump, they may have supplanted Florida and Ohio as the nation's premier presidential battlegrounds.

Sanders had a good showing in the industrial belt in 2016's Democratic primary, winning Michigan, Indiana and Wisconsin. But Hillary Clinton pounded him in Pennsylvania, 56% to 44%.

Some of Sanders' supporters from 2016 are still with him, and some are new. Stephanie Hosbach, a day-care worker who voted for Clinton in 2016's primary, drove an hour to see Sanders on Sunday and said her mind is made up to vote for him.

"I work two jobs," Hosbach, 34, said. "I feel like the minimum wage needs to be higher. We all struggle and you know Bernie's for those type of people."

Some of Sanders' supporters from 2016 have a taken a step back to study the big Democratic primary crowd.

One rallygoer, Fred Johnston, 45, said he backed Sanders in 2016's primary, but isn't certain who he will support in the 2020 primary.

"The election isn't until next year and there's a lot of choices," Johnston said. "I want to keep an open mind and hear them out. Right now Bernie's my first choice. ... I don't want to calcify my vote this early."

Trump's victory in Pennsylvania made him the first Republican to win it since 1988. Trump also knows the Midwest is vital to his re-election bid and is looking to repeat in states he won in 2016 and expand his territory.

The Sanders campaign said in a memo prepared in advance of the trip that the pathway to victory runs through the Midwest.

The memo said that Sanders has received donations from more than 8,000 people in Wisconsin, 14,000 in Michigan and 18,000 in Pennsylvania. Sanders was leading all Democratic candidates in fundraising.