Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) will campaign in five battleground states this week as he seeks to cement his support among white working-class voters.

Sanders has stops planned in Wisconsin, Michigan, Pennsylvania, Indiana and Ohio. President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE won all of those states in 2016.

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The Sanders campaign said in a statement that the Democrats’ “strongest path to victory in 2020 runs through the upper Midwest” and that Sanders is “by far the best-positioned candidate to win these states and defeat Donald Trump.”

At the campaign events, Sanders will focus on trade deals and union support, issues that should resonate with white, male blue-collar workers in the region.

Before Trump's victories, Michigan and Pennsylvania had not gone for the GOP nominee since 1988 and a Republican presidential candidate had last won Wisconsin in 1984. Former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE has been criticized for not campaigning in Wisconsin, which went for Trump by fewer than 25,000 votes. Democrats will hold their nominating convention in Milwaukee next year.

Indiana has been a more reliable state for Republican presidential candidates, though former President Obama squeaked out a victory there in 2008.

Obama won Ohio twice, and that state has long been a presidential bellwether. It is seen as strong territory for Trump and some observers believe it is moving toward Republicans.

Former Vice President Joe Biden Joe BidenOmar fires back at Trump over rally remarks: 'This is my country' Trump mocks Biden appearance, mask use ahead of first debate Trump attacks Omar for criticizing US: 'How did you do where you came from?' MORE, who along with Sanders is a top contender for the 2020 Democratic nomination, has also sought to burnish his credentials among blue-collar workers.

At a union speech Friday, Biden suggested that Trump succeeded in 2016 because the “sophisticated” elites had failed to understand the plight of everyday workers.

“How the hell do we get to the place where a lot of you think the rest of the country doesn’t see you, or know you?” Biden asked.

"All you're looking for is to be treated fairly, with respect, with some dignity,” he added. "Because you matter."