Senate Minority Leader Mitch McConnell, R-Ky., and other Republicans are coming to the rescue of Sen. Deb Fischer, R-Neb., who faces a legitimate threat to her re-election from independent Senate candidate Dan Osborn, a union leader and mechanic. 

Millions of dollars have been poured into Fischer's Nebraska Senate race in the last month as Republicans look to prevent an upset that could hurt their chances of taking the upper chamber's majority. 

The McConnell-aligned Senate Leadership Fund recently launched a $3 million ad buy in the state to shore up the Nebraska Republican's support. 

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"California and New York Democrats are putting crazy money into Dan Osborn’s campaign. They’re not going to succeed, especially as Nebraska voters learn about Osborn’s Democrat ties and Bernie Sanders' ideology. We’re just closing the gap a bit," Senate Leadership Fund President and CEO Steven Law said in a statement. 

The National Republican Senatorial Committee (NRSC) has also gotten involved, putting more than $500,000 into ad reservations as of the beginning of October, according to AdImpact.

Additionally, Fischer is getting help from well-known top Republican Sen. Chuck Grassley in neighboring Iowa. In a new radio ad, he tells voters, "This is your neighbor Chuck Grassley," adding, "my friend Deb Fischer needs your vote."

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Grassley's radio ad in Nebraska went out over the airwaves last week and will run through Election Day. The Iowa senator's five-figure ad buy covers 90% of the state, according to a source familiar with his political operation. 

The ad is on both FM and AM radio and plays during the University of Nebraska's football games to reach farmers, families and football fans. 

Osborn's popularity in Nebraska has appeared to take the Fischer campaign by surprise, given the seeming last-minute efforts to fortify her support. It's frequently difficult for independent candidates to gain traction, especially against an incumbent. However, without a Democratic candidate nominated in the Senate race, Osborn has a much larger pool of potential voters. 

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Republicans are heavily favored to regain the Senate majority in the next Congress, with expected gains in both West Virginia and Montana, as well as several other competitive races that could build a larger advantage for the GOP over Democrats in the upper chamber. 

However, those expectations rely on incumbents in relatively safe races winning their re-election matches. Fischer's Senate race has been shifted away from Republicans by top political handicapper the Cook Political Report two times in the past month, indicating a quickly tightening battle.

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In the most recent rating shift by Cook, the race is considered "Lean Republican," putting it in the same category as Sen. Ted Cruz's re-election bid in Texas against Rep. Colin Allred, D-Texas. 

Osborn has criticized Fischer in ads as being beholden to lobbyists and special interest groups that have donated to her, likening her to a race car driver with sponsors on her jacket. The independent candidate has claimed he would not caucus with Democrats or Republicans in the Senate if elected. 

Osborn has faced some controversy during his campaign, with revelations that groups backing him heavily in the election are funded in part by a dark money group that has received tens of millions in grants from billionaire George Soros' group, the Open Society Foundations. 

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