Explainer-Why we may not know the winner of the US presidential election on Nov. 5

FILE PHOTO: Republican presidential nominee and former U.S. President Donald Trump and Democratic presidential nominee and U.S. Vice President Kamala Harris are seen in a combination of file photographs taken in New York City October 17, 2024 and in Chandler, Arizona, U.S., October 10, 2024. REUTERS/Brendan McDermid & Evelyn Hockstein/File Photo

(Reuters) -The U.S. presidential election will take place on Nov. 5, but the winner of the razor-thin race between Democrat Kamala Harris and Republican Donald Trump may not be known for days after the polls close.

As ballots are counted, one candidate may appear to be leading based on early returns, only for a rival to close the gap as more votes are tallied.