In 2021, as the first Halloween decorations were coming out in Omaha, Neb., a mechanic named Dan Osborn led 500 of his fellow union members out of the Kellogg’s cereal plant on F Street and onto the picket lines.

The strike, which involved over 1,400 workers across multiple plants, would last for a difficult 77 days, through brutal storms and imported strikebreakers and the threat of summary dismissals, which drew the attention of President Biden. A first contract was soundly rejected by the union, then a second finally ended the walkout, just before Christmas.

Now Mr. Osborn, 48, is trying to do something considerably harder: win a United States Senate seat as an independent in the deep-red state of Nebraska.

Mr. Osborn’s long-shot bid to defeat Deb Fischer, Nebraska’s Republican senior senator, in November, or even come close, will test whether the rising power of an energized union movement can translate to high elective office during an election year when working class voters will likely decide the next president, and the direction of the country.

The rail unions of western Nebraska first approached him last year to mount a bid, and a December survey from a left-leaning group called Change Research put Mr. Osborn up on Ms. Fischer, at 40 percent over her 38 percent. It is a questionable result, as even Mr. Osborn’s supporters concede, but enough to capture imaginations in a one-party state that has long receded from the national political conversation.

With no Democrat in the race, the Nebraska Democratic Party is likely to endorse Mr. Osborn at a meeting on March 2, the party chairwoman, Jane Kleeb, said, though Mr. Osborn said he was not sure he wants that. The state A.F.L.-C.I.O. will back him at a gathering in late March, and national unions are taking a close look.

But can a union leader with no political experience find an agenda that transcends the two political parties and appeals narrowly to blue-collar wallets? And can that leader find the money to put that message out farther west, beyond the urban centers of Omaha and Lincoln?

“I’ve gone up against a major American corporation,” Mr. Osborn said as he cut into a steak Tuesday night. “I stood up for what I thought was right, and I won.”

The Fischer campaign appears to be treating Mr. Osborn as a nuisance, not as a serious threat to her bid for a third term.

“Deb Fischer has actual, strong and deep support all across the state, including 93 bipartisan county chairs and over 1,000 endorsements,” Derek Oden, her campaign manager, said. “She is proud of her longstanding support from members of Nebraska labor unions and is willing to work with any Nebraskan to make life easier for working families across our state.” The campaign cited three firefighters’ unions as well as the carpenters and electricians who backed her six years ago.

Mr. Osborn’s attempt to leap from leader of his local to member of the U.S. Senate has little precedent, almost akin to the five failed presidential bids of the celebrated labor leader Eugene V. Debs early last century.

Union members in other states have made the jump to elective office, like Tim Walz, the governor of Minnesota, and Brandon Johnson, the mayor of Chicago. The New Jersey A.F.L.-C.I.O. has trained 1,300 members to run for office over the past 27 years, with a success rate of 76 percent.

Those seeking office receive instruction in campaigning, opposition research, election law, campaign finance, public speaking and handling the press, said Charles Wowkanech, the president of the New Jersey A.F.L.-C.I.O. In a heavily unionized, Democratic state, the program identifies and contacts every union member in a given district, and, often, they account for more than enough votes to win.

That is not the situation in lightly unionized Nebraska, where 9.4 percent of workers are represented. But even in New Jersey, where 17.3 percent are, the highest office sought has been the U.S. House of Representatives, where a union electrician who went through the program, Donald Norcross, holds the First Congressional District.

“We modeled the labor candidate program after apprenticeship programs,” Mr. Wowkanech said. “You don’t start as a journeyman earning top rate. You work your way up.”

In 2018, Randy Bryce, who is known as “Iron Stache,” captured liberal imaginations and a lot of money as an iron worker (and the secretary of the Racine County Labor Council) running for the house seat of retiring Speaker Paul D. Ryan in Wisconsin. He lost by more than 12 percentage points.

“There definitely are ways to reach across the aisle, but it’s getting rougher every year, that civil divide,” Mr. Bryce said. “We’ve got to find reasons to talk to each other again, and working people running for office is a start.”

Soft-spoken and earnest, Mr. Osborn is not exactly Norma Rae, the brash protagonist of the 1979 film that dramatized the plight of workers and the struggle to organize in the South. Kellogg’s management fired him a year ago, accusing him of watching Netflix while on the job, a charge he and his friends called trumped up. He is now an apprentice with the steamfitters’ union, still working on heating and air conditioning systems as he gets his campaign in gear. He’s also a father of three children between the ages of 16 and 21. His wife is the general manager of a bar and grill in Omaha.

“He’s not pounding his first on the table,” said Danny Begley, an Omaha City Council member and vice president of the International Brotherhood of Electrical Workers Local 1483. “He’s measured. He’s calculated.”

Mr. Osborn, who said he was a Democrat until 2016, wants to run on a narrow platform with what he hopes is extremely broad appeal: legalize marijuana (at least for medical use), raise the minimum wage nationally, secure abortion rights, protect gun rights and expand laws to facilitate union organizing. He condemns the inflation of the Biden era, but blames corporate greed and price gouging. He speaks of the U.S. border in distinctly Republican ways.

“Without borders you don’t have a country,” he said, though he added that once the border is closed, Congress should explore ways to legalize some undocumented workers already in the U.S.

Early in Israel’s war in Gaza, campaign advisers told him to put out a statement staking a position. He refused, saying that it was not an issue he wants associated with his campaign.

“Dan has to get a message out that transcends political lines and goes to their pocketbooks,” said Josh Josoff, an ally with the International Union of Elevator Constructors. “Don’t let the wedge issues pull you away.”

On the one issue he most certainly will not be able to escape, the presidential campaign, he seemed genuinely befuddled. Nebraska is overwhelmingly behind Donald J. Trump, as is Ms. Fischer. Mr. Osborn is not, a potential campaign killer this November. But he is not backing President Biden either.

“I think they’re both too old; I think they’re both incompetent,” he said, finally settling on a position. “There’s a good chance I won’t vote for president.”

“He’s got a hard-core economic agenda, and he has a really unique profile,” Mr. Kerrey said. “You can’t say, ‘Well, what do you know about what we’re going through?’ because he does. He knows that the rules don’t work for working people.”

But Nebraska is stacked against Mr. Osborn. West of Lincoln are some of the largest rail yards in the country, but the freight rail companies, backed by Nebraska Republicans, have manhandled the rail unions, which were the first to ask Mr. Osborn to run after a new contract failed to grant their demand of seven paid sick days a year. Such unions may have limited power to deliver North Platte and points west.

The state’s junior senator and former Republican governor, Pete Ricketts, is the other obstacle to Mr. Osborn’s bid. He comes from a family of financiers worth billions of dollars, and he is more than willing to spend it.

Just ask Crista Eggers, who has been trying to legalize medical marijuana since 2019 to treat her son, Colton, who suffers daily epileptic seizures that his physicians believe are treatable with cannabis. Only three states still prohibit medical marijuana, though polls suggest 70 percent to 80 percent of Nebraskans support it. One of those people opposed is Mr. Ricketts, who declared as governor, “If you legalize marijuana, you’re going to kill your kids.”

In 2020, Nebraskans for Medical Marijuana got 197,000 signatures, in more than enough counties to get a legalization referendum on the ballot. But the Nebraska Supreme Court struck it from consideration on a technicality. Supporters tried again in 2022 but came up short of signatures. Ms. Eggers and her group are now at it again, hoping for some synergy with a ballot drive to protect abortion rights and with Mr. Osborn’s campaign, though the group is prohibited from endorsing him.

A problem for Ms. Eggers, and for Mr. Osborn, is money. Signature drives are costly, and 90 of Nebraska’s 93 counties are rural, adding to the challenge. Mr. Osborn himself has little name recognition statewide, and would require an introduction in the form of television ads and a robust campaign schedule, both expensive endeavors. Union supporters are optimistic that Mr. Osborn’s message resonates against Ms. Fischer, if he has the cash to get it out.

“We just need to push past the Republican and Democrat thing, these teams we’re on,” said Josh Dredla, a friend of Mr. Osborn’s who was on the Kellogg’s picket lines.

Mr. Osborn said at a minimum the campaign needs to raise $2 million. So far, he’s raised just over $200,000.

Ms. Fischer ended 2023 sitting on a war chest of close to $3.3 million.