Under the country’s electoral college system, each state has a fixed number of “electors.” The number of votes each state has is determined by the number of members of Congress representing that state. For example, a state with three House members and two senators has five electoral college votes. In almost every state, all of the state’s electors vote for the candidate who wins the most votes in that state, a process known as “winner-take-all.”

But that’s not the case in Nebraska, where three of the state’s five electors vote based on the results of their precincts.

In 2020, Joe Biden lost to then-President Donald Trump in Nebraska by 19 points. But Biden defeated Trump by 6.5 points in the state’s 2nd District, which includes the state’s largest city, Omaha. As a result, four of the state’s five electoral votes went to Trump, while one went to Biden.

Polls show Harris leading the 2nd District this year, and Republicans are eager to avoid a repeat of 2020. On Wednesday, Sen. Lindsey Graham of South Carolina skipped the Senate vote to travel to Lincoln, Nebraska’s capital, where he lobbied state lawmakers to move the state to a winner-takes-all model in the final weeks before the election.

“I was happy to get out there and talk about the world as I see it,” Graham told CBS News on Thursday. “I hope that the people of Nebraska will understand that this could come down to a single electoral vote. And I just don’t believe a Harris presidency is good for Nebraska.”

The Mathematics of the Electoral College

According to the Electoral College, a candidate must receive 270 votes (a majority of the 538 total electors) to win.

Seven states are widely considered to be the key swing states. Three of them are traditional “blue wall” states that have historically voted Democratic but which Trump narrowly won in 2016: Pennsylvania, Michigan and Wisconsin.

The other four are the “Sun Belt” states of Nevada, Arizona, Georgia and North Carolina. Biden won Nevada, Arizona and Georgia in 2020, but Trump generally leads in those states’ polls this year.

And then there’s Maine, a Democratic-controlled state that distributes its electoral votes the same way as Nebraska. Trump won Maine’s 2nd District handily in both 2016 and 2020, and while some polls have shown Harris ahead of Trump there, he’s generally considered more likely to win that district, which would give him one of the state’s four votes.

Maine earlier this year threatened to switch to a winner-takes-all system for electoral college votes if Nebraska did the same. But unlike Nebraska, doing so before the election is likely too late — it would require two-thirds support from the Maine legislature, which Democrats don’t have.

How One Vote Can Change Elections

As Graham noted, there is only one electoral vote at stake in Nebraska. But that one vote could make the difference between a Harris victory and a tie.

Under current rules, if Harris lost all of the Sun Belt states and Maine’s 2nd District, but won all of the blue-walled states plus Nebraska’s 2nd District, she would get exactly 270 votes. That’s enough to become president.

But without that one vote from Nebraska, Harris would have to win at least one of the Sun Belt states or Maine’s 2nd District.

Otherwise, it’s a 269-269 tie — a result that would send the election to the House of Representatives, where a candidate must win the support of at least 26 state delegations to win. In such a scenario, Trump would have a significant advantage — Republicans would likely control most of the state delegations, even without a majority.

That’s not to say it’s impossible for Harris to win outside the blue wall. The vice president generally has a lead in Nevada polls, with Trump narrowly ahead in the other three states. Harris’ campaign manager, Jen O’Malley Dillon, wrote in a memo earlier this month that while members of the campaign considered themselves “clear underdogs,” they believed Harris had “multiple paths to 270 electoral votes.”

But a change in Nebraska’s electoral college split would make an already tough election even tougher for Harris, as she would no longer be able to rely on the blue wall to win.

It’s unclear whether Nebraska lawmakers will move forward with the winner-takes-all system. Republican Gov. Jim Pillen supports it, but there weren’t enough votes in the state’s unicameral legislature to pass the change earlier this year.

According to the Nebraska Examiner, some of the former opponents may be coming around and the GOP campaign is still going strong.