CLAYCOMO, Mo. — Dianne Maxwell enjoyed a comfortable life in this suburb north of Kansas City, until her husband lost his job as a printer last year.

He's since found work as a long-haul truck driver, but money is tight.

So when a Bernie Sanders volunteer knocked on her door Saturday, she had one issue on her mind. "What matters to me is the middle class," she said, adding that her vote in Tuesday's primary hinges on which candidate will do more to improve health care and take on the burgeoning national debt.

The battle for the Democratic presidential nomination shifted to the Midwest this week with a showdown over which of the top two remaining candidates has the strongest appeal among working-class whites — the voters seen as crucial to the party's hopes of making gains in this region and beating President Trump in November. The duel will play out largely in Michigan and Missouri, which hold primaries along with four other states Tuesday — the next in a string of big primary days that could determine a presumptive nominee in a matter of weeks.

Sanders dominated this group in his 2016 Democratic primaries against Hillary Clinton, including in his stunning victory that year in Michigan. His allies have argued that many working-class voters in the region drawn to Sanders's populist message wound up staying home or backing Trump in the general election, sparking the president's decisive wins in Michigan, Wisconsin and Pennsylvania.

But former vice president Joe Biden, a native of Scranton, Pa., who has presented himself as a son of the Rust Belt and a champion of the middle class, has argued that he is more suited to win these voters back. Exit polls from last week's Super Tuesday contests, in which Biden surged to take a national delegate lead, showed that he beat Sanders among non-college-educated whites by four points.

"Missouri is critical as a test of Sanders's ability to hold on to white working-class voters," said Dave Robertson, chair of the political science department at the University of Missouri at St. Louis. "If he can't do this in Missouri, he can't do it in the big Midwestern states coming up — Wisconsin, Ohio, Pennsylvania — that will be key to winning the general election in November."

In Missouri this weekend, Biden touted his working-class roots. Fresh off his victories last week and with a national delegate lead, Biden held a campaign rally Saturday at the National World War I Memorial and Museum in Kansas City, with workers from firefighters and electrical unions carefully arrayed behind him in the setting sun.

“All those who’ve been knocked down, all those counted out and all those who have been left behind — this campaign is your campaign,” he said, drawing cheers with a common refrain from his stump speech.

He often recalls personal stories that shaped him from his childhood in Scranton. He also reflects on the tragedy that befell him as a young senator-elect, when his wife and baby daughter were killed in a car crash.

Even Biden’s opponents say his personal narrative appeals to voters. “He has a compelling personal story. He’s very likable, very decent, and people trust him as vice president. He’s certainly a formidable opponent,” said Rep. Ro Khanna (D-Calif.), a Sanders supporter. “But I don’t think a return to normalcy is sufficient.”

Biden’s wife, Jill, appeared at events in St. Louis, Columbia and Kansas City on Monday, according to the campaign. Union workers will be knocking on doors throughout the Midwest for Biden, and surrogates such as Sen. Thomas R. Carper (D-Del.) joined picketing Teamsters in Michigan over the weekend.

Walt Landis, 59, a draftsman and retired farmer from Faucett, Mo., said he supported Biden in part because he thinks Biden’s establishment ties mean he will be able to cooperate with the Republicans in Washington.

Sanders, he said, is too much of an iconoclast.

“He’s a bit too militant for me,” Landis said. “We don’t need a revolution — we had that argument in 1776.”

Sanders and his volunteers, meanwhile, have tried to keep the conversation focused on policy. In recent days, the candidates have sparred over Social Security and Biden’s past support of trade deals such as the North American Free Trade Agreement, or NAFTA.

On the stump, Biden, 77, the son of a used-car salesman, calls himself “Middle Class Joe.” Sanders, 78, touts his decades of work on liberal causes and proposals such as the $15 minimum wage and the cancellation of student debt.

“He’s the most pro-worker, pro-union candidate we’re ever going to have, at least in my lifetime,” Bobby Cervantes, 31, a graduate teaching assistant at the University of Kansas, said as he canvassed for Sanders on Saturday in Claycomo, a working-class neighborhood of modest ramblers and split-level homes near a Ford assembly plant. He tucked literature in doorways that outlined Sanders’s plans for Medicare-for-all, fair trade and worker rights.

Maxwell, 54, a former Kmart worker, said she was worried about empty promises from both candidates when the Sanders volunteers knocked on her door.

“Who am I going to give my trust to?” she wondered.

“Bernie wants to make sure everybody gets free college and to get rid of student loan debt,” said campaign volunteer Hannah Allison, 32, a teaching assistant from Lawrence, Kan.

“But how are we going to pay for it?” Maxwell countered. “He hasn’t come up with a concrete plan. Kind of like Trump — build the wall and have Mexico pay for it.”

Her neighbor Nathan Clapham, 26, a college student, said he was voting for Sanders. He said he was raised in poverty, the child of itinerant construction workers, and now lives with his sister because he can’t afford an apartment of his own.

“Bernie’s rhetoric of populism hits the same kind of notes as Trump’s, so he’ll be more appealing to working-class people,” Clapham said. “Unfortunately, every single person who’s going to get up on that stage is pushing 80 years old.”

“But at least Bernie wants different things,” he continued. “Biden is literally saying we’re going to keep doing the same things we’ve always done. It’s not working.”

Scott Clement in Washington contributed to this report.

Tuesday's primaries

Six states will vote in presidential primaries. Poll closures are listed in Eastern time.

State Delegates Closing
Mississippi 36 8 p.m.
Missouri 68 8 p.m.
North Dakota 14 8 p.m.
Michigan 125 9 p.m.
Idaho 20 11 p.m.
Washington 89 11 p.m.

For live results and analysis, visit wapo.st/elections