In a close race, the presidential election could be decided by an unlikely spot: Nebraska’s Second Congressional District, including Omaha and most of its suburbs.

If the race is decided there, Joe Biden appears to have the advantage, according to a New York Times/Siena College poll. He leads President Trump by seven points, 48 percent to 41 percent, among likely voters in the first nonpartisan survey of the district so far this year, according to FiveThirtyEight.

Unlike most states, Nebraska awards its Electoral College votes by congressional district. Under state law, the winner of Nebraska receives two votes, and the winner of each district receives one. Every other state, except Maine, awards its electoral votes on a winner-take-all basis. As a result, Nebraska’s Second can play a potentially decisive role in an extremely close election: one decided by one vote in the Electoral College.

Nebraska’s Second has long loomed as a potential vulnerability for the president. The district is traditionally Republican, but Mr. Trump carried it by only two percentage points in 2016. The district was even closer than familiar battleground states like Arizona or North Carolina.