A seemingly non-competitive Senate race in deeply Republican Nebraska is no longer a safe bet for two-term incumbent Sen. Deb Fischer -- the dynamics jolted by the late-stage insurgence of independent Dan Osborn, who, if successful, could be the deciding factor on which party has control of the chamber, where Democrats currently hold a razor-thin 51-49 majority.

"I hate to call it like I'm trying to call a Nebraska football game, but I would say I'm gonna win pretty substantially. People are ready for a change. People are sick of the status quo," Osborn told ABC News in an interview.

Fischer holds a slight edge in polling -- and to be sure, Nebraska has reliably voted for Republicans in presidential races over the past several decades, and Trump handily won the state in 2020 by nearly 20 points and has endorsed Fischer -- but national groups are flooding the zone with last-minute investments.

The GOP's Senate campaign arm, the National Republican Senatorial Committee, recently placed a $172,000 ad buy with Fischer's campaign, according to AdImpact. And conservative super PAC Heartland Resurgence has invested nearly half a million dollars in ads opposing Osborn, although there has also been more than $1.6 million in outside spending supporting Osborn, according to an analysis by OpenSecrets.

"At this particular moment, Nebraska is the second-closest Senate race in the country, according to 538's polling averages. If you had told me a year ago that Nebraska was going to be Republicans' most vulnerable Senate seat this year, I'd have laughed at you. But I still think there's reason to think Osborn will have trouble closing the deal," 538 Senior Editor and Senior Elections Analyst Nathaniel Rakich told ABC News.

Fischer leads Osborn by a little more than 3 points per 538's average of statewide polling. Fischer is aware of the competition and told ABC News she feels "good" about her chances (pointing out her near 20-point win against Democrat Bob Kerrey in 2012) but is "taking [the polling] seriously"

"I run like I'm 20 points behind. I am always in the state, even when I am not in cycle, I am back in Nebraska. And Nebraskans know that my last opponent I beat by 20 [points]," Fischer told ABC. "When Nebraskans see who this guy really is, we're going to be fine."

Also reflected in that polling average, Rakich points out, is that about 18 percent of Nebraskans remain undecided in this race -- and he suspects many of them are Republicans, who will likely prefer Fischer come Election Day. But with Osborn within striking distance, his victory could transform him into a serious Senate power broker, and with that, invite some chaos.

"You could have a scenario where you have Osborn plus 50 Republicans and 49 Democrats, or Osborn plus 50 Democrats and 49 Republicans. In that case he could literally decide who controls the chamber by picking which side to caucus with. He could also try to convince someone like Lisa Murkowski to join an independent bloc within the Senate that could flip back and forth between Republicans and Democrats depending on the issue," Rakich explained.

Despite his potential power to help them maintain the Senate majority, national Democrats have been hesitant to embrace Osborn directly.

Last Thursday, Democratic Senatorial Campaign Committee Chair Sen. Gary Peters, at an event at the National Press Club, stressed he was "not engaged" in the Nebraska Senate race "in any way" when asked about the closer-than-expected contest.

"So we do not have a Democrat running in Nebraska, and so I'm not engaged in that. In any way."

Peters doubled down: "I'm not engaged. I don't pay attention to Nebraska. I got a lot on my plate right now. I got a lot of states that I'm watching. So I have -- sorry, can't give you a better answer, but we don't have a Democrat in Nebraska, so I'm not involved," Peters said.

In 2021, Osborn, a Navy veteran, led employees of a Kellogg's plant in Omaha, where he had worked since 2004, on a strike that extended around the country, and he has ridden his blue-collar roots to unexpected popularity in his race against Fischer.

"He's had over 140 public events this year. He has spent a lot of time blanketing the state, criss-crossing the state, town halls, meet and greets. No event is too small. He's been really doing the kind of old-fashioned voter-by-voter engagement, and people appreciate that," a person familiar with Osborn's campaign told ABC News in explaining the candidate's appeal.

Being on the campaign trail has been an adjustment for the longtime steamfitter and mechanic -- a political newcomer.

"I've been a person who's done nothing but go and clock in at the same factory… wrenching on the same machines for over 20 years," Osborn said. "And I've always worked seven days a week, a lot of 12- to 16-hour shifts. So I've never been able to branch out to Nebraska and see it for what it is." (Roll Call reported in May that Osborn is currently taking a salary from the campaign.)

"Nebraska is a gem," Osborn added. "I really had no idea, but I got to fall in love with the state, so it's been a lot of fun."

When Fischer declined to participate in a televised debate, Osborn took a one-man show on the road, holding at least one town hall with an empty chair to represent Fischer's absence. (Fischer said she was prioritizing meeting with Nebraskans.)

In a recent ad, Osborn, standing in a warehouse with factory equipment behind him, compares Fischer to a NASCAR driver, with the logos of corporations on her jacket, to convey that the senator is too beholden to big business donors.

With the balance of power in the Senate at stake, Osborn has repeatedly faced questions about which party he would caucus with if he makes it to the chamber.

But, unlike Vermont independent Sen. Bernie Sanders, who caucuses with Democrats, Osborn has insisted he won't link arms with either party.

Osborn told ABC News he would "certainly, considering caucusing with either party that has control of the Senate, because that's how I'm going to best deliver for Nebraskans… I would consider caucusing with whoever has control, only if my idea fails, but certainly I want to create an independent caucus, a caucus that is going to benefit everyday people." (Osborn's campaign later told ABC News he was referring to working with both parties and still does not plan to caucus with either party.)

Some have speculated that Osborn would have to caucus with one party or another in order to be assigned to committees. There are possible ways where an independent could make it onto committees without doing so -- but there is little precedent and what would actually occur could depend on the final makeup of the Senate.

Osborn told ABC News he is not too concerned about that, and said he understands that members of Congress also need to spend much time fundraising, in part to help them get committee assignments. "I'll dial for dollars and I'll buy my committee assignments… I certainly, again, want to challenge the system. But, I don't want the people of Nebraska to suffer, either, so I'll figure that out as we go."

Osborn also added that there's nothing "written in stone" about needing to caucus with a specific party, and if he ends up becoming a swing vote in the Senate, "that's going to give me a little bit of swagger, right? That's going to make people want to have to work with me, and I'll certainly have no issue making deals to get on committees, but we'll cross that bridge when we come to it."

As for what policies he supports, Osborn told ABC News that on abortion access, he would support codifying Roe v. Wade -- as an issue of individual freedoms and a way to return women's health decisions to themselves. He also supports a secure U.S. border and protecting the 2nd Amendment while allowing for "reasonable gun safety measures," according to his campaign website.

Fischer told ABC News she finds Osborn's independent label disingenuous, noting, for example, his stance on eliminating the legislative filibuster.

"Nebraskans don't know him, and when they realize who he is and what he stands for, those are beliefs that are not in tune with the majority of Nebraskans," Fischer said in a phone interview with ABC.

Fischer herself sits on six Senate committees, including the high-profile Appropriations and Armed Services committees, and noted that Osborn's resistance to say who he might caucus within the chamber is evidence he is trying to make inroads with independent voters while not being honest about his intentions. She added that the fate of Senate control is "first and foremost" at stake in this election.

"Nebraskans are not going to be fooled by this. Nebraska is a conservative state. I am a conservative senator, and they're going to realize this guy is just out there talking about debate and town halls, and he's not talking about anything that truly impacts the lives of the people of this state," added Fischer.

National progressive organizing group Indivisible said in a recent fundraising email that it may try to indirectly support Osborn.

"This race is ripe for disruption, and Dan Osborn, running as an independent, isn't accepting any Democratic Party support... That's actually a strength in Nebraska. He needs grassroots, Nebraskans-to-Nebraskans mobilization," Indivisible Chief Campaigns Officer and co-founder Sarah Dohl wrote in a recent fundraising email.

"I really believe that our tools could tip the scales."

Randall Adkins, a political science professor at the University of Nebraska-Omaha, told ABC News that the national Democratic Party's public spurning of the race, and Osborn's stated refusal to accept Democratic Party support, is likely a strategic move.

"If they come in and help Osborn, if a Democratic group comes in and helps Osborn, that could potentially hurt him with voters that might be politically independent and likely to vote for him, because they're politically independent,' Adkins said.

While most national Democratic groups may not be openly joining the fray, the state's Nebraska Democratic Party is outwardly supporting Osborn's candidacy, including promoting him in mailings to voters and press statements -- although the party says it is not formally endorsing him, out of respect for his decision to not want any party endorsements.

But that understanding came after a few bumps in the road. The state party said in May that Osborn courted the party's endorsement and ballot line, but then changed his mind. (Osborn's campaign says he never planned on running as a Democrat at any point.)

"The relationship obviously got strained when Dan changed his mind and then left us in a difficult situation. But [we] as a party, you rise above a lot of differences in politics and a lot of things that get thrown your way," Jane Kleeb, the chair of the Nebraska Democratic Party, told ABC News.

The party had considered fielding a write-in candidate for the race; Kleeb said the party opted against that in order to allocate more resources to U.S. House and state legislature races, Kleeb said.

"He has Republicans being willing to switch parties on the ballot because they're not totally thrilled with [former President Donald] Trump at the top... and he's a great candidate. He is a retail politics candidate -- in the parades, in the town halls and the bars, he is just visiting with voters, and then they're going and talking to their friends and family," Kleeb added.

Kevin Smith, who teaches political science at the University of Nebraska-Lincoln, says Osborn's backstory is also sparking voters' interest.

"He's kind of a blue collar guy, military background, bootstrapped his way up -- has successfully managed to put out an image that he's not beholding to either political party," Smith said.

That independent image could matter in Nebraska, where the image of the Democratic Party is "pretty tattered" outside of larger urban centers; it may also tap into people's thirst for an alternative to the major parties, Smith said.

Both Smith and Adkins emphasized that Fischer's incumbency gives her an advantage, as well as the sheer number of more Republicans registered in Nebraska than Democrats or independents, and Donald Trump's popularity in much of the state.

Osborn thinks he can escape that gravity.

"Trump's got nothing to do with Osborn. I'm an independent… So why would somebody vote against the Republican and go for an independent? But I think ultimately, it's my broad stroke message. And my broad stroke message is that both parties are corrupt," he said, adding that he also thinks people will appreciate that he is not taking corporate money and that his campaign is "powered by the people."

Osborn said he has refunded some contributions from donors he does not want to take money from, although he declined to name anyone specifically. Recent campaign finance filings show that his campaign refunded $2,250 in donations.

Adkins added that Fischer might lose Douglas County -- where Omaha is located -- and some other liberal-leaning areas of the state, but could run up a strong margin by winning every other county in the state.

And Smith noted the precarious position of the Senate chamber if Osborn pulls off a "political earthquake."

"If Osborn were to pull off what really would be kind of -- at least in Nebraska -- a bit of a political earthquake, what does he do when it gets to the Senate? I mean, does he caucus with the Democrats? Does he act as a genuine independent and doesn't caucus with either party?" Smith asked.

There's a novelty to Osborn's candidacy as well for Nebraska -- with his momentum coming on the coattails of the Electoral College vote controversy, which also briefly thrust the state into national attention. Separately, Democrats also hope that state Sen. Tony Vargas can flip the state's 2nd Congressional District; Vargas has led slightly in recent polls.

"This is sort of a new thing for Nebraska. We've not had, or we've not seen anybody run for political offices as an independent and have relative success," Adkins said.

As for how Nebraskans are feeling about the additional attention?

"There's definitely a sense of, in one sense, it's kind of like, finally, it's nice to get some attention, because then the interest in the perspectives of Nebraskans will be folded into the national conversation," Smith said, when it's usually ignored as part of "flyover country."

ABC News' Isabella Murray and Allison Pecorin contributed to this report.