You might be excited about Election Day, dreading it, or desperate for it to be over.

Regardless, it is here.

But the end of this high-drama presidential campaign on election night may not bring immediate clarity about who has won.

The race itself is unlike any other, pitting former President Donald J. Trump, a man who has essentially been running for president for nine years, against Vice President Kamala Harris, a woman who has been running for about 16 weeks. The contest, which began as a rare rematch between Mr. Trump and President Biden, was reset after a televised debate that ended Mr. Biden’s bid for re-election and paved the way for Ms. Harris’s midsummer ascendance — and it took a violent turn when two would-be assassins made separate attempts on Mr. Trump’s life.

More than 78 million people have already voted. And as we head into the final day of voting, polling suggests that two candidates who could not be more different — who fundamentally disagree on weighty matters of the economy, women’s rights and the very purpose of government — are locked in an excruciatingly tight contest, with all seven battleground states still in play.

It could take days or even longer to know who wins. Here’s what to watch as the counting begins.

When will the race actually end?

Polling shows Ms. Harris and Mr. Trump deadlocked in nearly all of the seven swing states. So the first thing we’ll glean from the returns on Tuesday night is not who will win — but just how close the battle is shaping up to be, and how long it might take to determine the winner.