The candidate who receives 270 electoral votes will be the one who wins the presidency, and the fate of Harris and Trump will likely depend on the results in the seven battleground states: Arizona, Nevada, Georgia, Michigan, Wisconsin, Nevada and North Carolina.

Here are some of the ways Harris could reach 270 that seem most plausible given past election results:

Mr. Biden won six of the battleground states in 2020: Arizona, Nevada, Georgia, Michigan, Wisconsin and Pennsylvania. In total he won 306 electoral votes. Heading into Election Day 2024, polls in these states are close to zero.

If Harris wins Michigan, Pennsylvania and Wisconsin, the “blue wall” Midwestern states that Mr. Biden captured in 2020, and gets three of Maine's four electoral votes, but she loses Arizona, Nevada and Georgia, that would not make Harris eligible Bring White House.

In this hypothesis, Trump would also retain all of the states he won in 2020 and four of Nebraska's five electoral votes, as he did four years ago.

That scenario would put Harris at 269 electoral votes — a slim chance of keeping the White House under Democratic control. To get to 270, Harris would have to win a congressional district in Nebraska that includes the city of Omaha. The state allocates some of its electoral votes by congressional district and wins Nebraska's district based in Omaha that Mr. Biden was captured in 2020 but Trump held in 2016 would make Harris president.

— Hunter Woodall and Olivia Rinaldi