In presidential election years, an area of deep-red Nebraska nicknamed the “blue dot” can draw plenty of attention. The state awards an Electoral College vote to the winner in each of its congressional districts, and its lone swing district could decide an exceptionally close White House race.

Now the district, which includes Omaha, is getting a turn in the spotlight in this year’s midterm primaries. Representative Don Bacon, a moderate Republican who has held the district for nearly a decade, is retiring, and Democrats competing to replace him have crowded into the race.

Although the district has long been in Republicans’ hands in Congress, it has gone to Democrats in three of the last five presidential races, giving it its nickname.

One of the main issues animating this year’s Democratic primary is a suggestion that a victory by a leading candidate could ultimately spell an end to the blue dot’s unique role in presidential contests. Here’s why, and what else you should know ahead of the primary on Tuesday:

What is the blue dot?

The blue dot refers to the speck of blue on the map that the Omaha-area Second Congressional District can create when it votes for Democrats in presidential elections.

The nickname took off in 2024, as blue dots popped up on yard signs, light poles and T-shirts.

The district went for Kamala Harris in 2024, Joseph R. Biden Jr. in 2020 and Donald J. Trump in 2016. Mitt Romney won the district in 2012. Barack Obama’s victory there in 2008, the first by a Democrat in four decades, caused some to call the area “Obamaha.”

Nebraska and Maine are the only states that split their electoral votes.

Who is running in the Democratic House primary?

City Councilman Brinker Harding of Omaha, a friend of Mr. Bacon who has inherited much of his campaign team, is running unopposed in the Republican primary.

But the Democratic primary is competitive, according to Democrats in the state. The leading candidates are State Senator John Cavanaugh; Denise Powell, a political organizer; and Crystal Rhoades, a court clerk.

Mr. Cavanaugh, the son of a Nebraska congressman, has support from the Congressional Progressive Caucus, labor groups and state lawmakers. He has led the race in limited public opinion polls.

How does the blue dot debate factor in?

Ms. Powell and Ms. Rhoades have sought to halt Mr. Cavanaugh’s rise by warning voters that if he is elected and vacates his legislative seat, Republican state lawmakers might be emboldened to pass a law shifting Nebraska to a winner-take-all electoral system. (In 2020, Donald J. Trump’s allies unsuccessfully pushed Nebraska lawmakers to abandon the unique electoral system.)

Gov. Jim Pillen, a Republican, would be able to appoint a replacement for Mr. Cavanaugh, potentially allowing Republicans to add another legislative voice opposing the blue dot system.

Other members of both parties say it is unlikely that the blue dot is in immediate peril. Republicans already have a supermajority in the State Legislature and have held off from changing the electoral system, apparently because Republicans in the Omaha area enjoy the district’s swing status in presidential years.

“They control all of the levers of power in the state of Nebraska, and they haven’t eliminated the blue dot,” said Mr. Cavanaugh, who devotes a section of his campaign website to the blue dot issue.

He said Democrats could easily offset the loss of his seat in the fall, predicting Democrats were on track to gain at least five state legislative seats.

But Ms. Powell said Mr. Cavanaugh was “asking voters to take a risk.”

Ms. Rhoades said, “We should not gamble.”

Mayor John W. Ewing Jr. of Omaha, a Democrat who supports Ms. Rhoades, said the blue dot was a nonissue. Mr. Cavanaugh’s victory would not “change the dynamics to the point that the blue dot could be eliminated,” Mayor Ewing said.

What does the departing congressman say?

Mr. Bacon said that the blue dot was “probably” not at risk, but that it was “not a made-up issue.” Even if it is unlikely that Democrats would simultaneously win the House seat and lose ground in the State Legislature, elections are unpredictable, said Mr. Bacon, who won re-election in 2024 even as Mr. Trump lost the district.

“That’s the problem,” he said of Mr. Cavanaugh’s challenge in fending off the attack. “You don’t know how the election’s going to go.”

What does the race mean in the battle for the House?

As the American political battleground has been winnowed by polarization and gerrymandering, the dwindling swing districts have grown in importance for both parties.

Nebraska’s Second District has been trending to the left, and Democrats see it as a prime pickup opportunity this fall, given Mr. Bacon’s retirement. The district is one of the just three represented by a Republican where Ms. Harris won in 2024. Still, outside of a single term from 2015 to 2017, Republicans have held the House seat since the mid-1990s.

This Democratic primary race has been deluged by spending from outside groups, including one aligned with Speaker Mike Johnson, Republican of Louisiana.