AMNA NAWAZ: The 2026 campaign has been the most expensive in U.S.

history, and it's all leading to tomorrow night, when the votes are counted.

Deema Zein has a look at what happens next.

DEEMA ZEIN: Millions of votes have been cast in this midterm election.

Traditional battlegrounds have expanded in the fight to control Congress.

It all comes down to one question: Who won?

This year, the "News Hour" is once again relying on the Associated Press to call winners in critical races.

For a closer look at how the AP makes those race calls, I'm joined by David Scott, V.P.

of election services at the Associated Press.

David, thanks for joining us.

DAVID SCOTT, Vice President of Election Services, Associated Press: Happy to be here.

DEEMA ZEIN: So I want to jump right in.

People watching results on election night want to know the winner.

So tell us, how do you know when the race is over and which candidate won?

DAVID SCOTT: So the thing that we're looking at primarily is the vote count.

We are reflecting the choices that Americans have made at the ballot box as they make their choice about who they want to lead the country, who they want to represent them in Congress or in the statehouse.

And so we start there.

And, really, the question we're asking ourselves is, are the trailing candidates or a trailing candidate able to catch the leader?

And when we have determined, based on all of the evidence, primarily the vote count, but other things that we take into account, what happened in the advance vote, what's the history of a state, what our poll shows about what took place and what voters were thinking about on election night, but really the vote count, when we see and we are certain that the trailing candidate can't catch up, that's when we declare a winner.

DEEMA ZEIN: And who makes that ultimate decision?

DAVID SCOTT: We have got a big team at the Associated Press that makes up our decision team.

And they're all journalists.

They are people who cover politics.

They are data analysts.

They are experts in political science.

They are folks who study this year-round full-time.

We have folks who focused on turnout and what the expected vote it is.

What's the denominator?

How many votes are going to be cast in this election?

And then, of course, the numerator, what are each candidate getting?

And, again, we're trying to answer that question.

When we look at all the votes that have been counted so far, what do we see about what's outstanding?

And has a candidate reach the point where none of the others are able to catch them and they will be the winner?

And that's when we declare a winner.

DEEMA ZEIN: And not until that moment.

DAVID SCOTT: Not until that moment.

Our certainty is our standard.

We're not trying to be first.

We're not trying to race to a decision.

We are looking at what's coming in.

But we also feel an obligation to let an the voters know, to let America know, this is who you have chosen to lead.

And so we're being swift, but always focused on accuracy first.

Our standard is certainty.

We are certain when we declare a winner that the trailing candidates can't catch up.

DEEMA ZEIN: Do bad calls actually happen?

And, basically, why should Americans trust AP to get it right?

DAVID SCOTT: We have been doing this literally since the founding of the Associated Press; 1848 was the first time that we counted the vote and declared winners two years after the founding of a cooperative.

It's part of who we are as a news organization.

We think that the choices that Americans have made is a news story.

It's really important.

In this year's primaries, we declared winners in more than 11,000 races.

And we made three mistakes.

And one was because of bad information from election officials, for example.

And another one was because of a technical problem.

So they do happen, but they're very rare.

DEEMA ZEIN: David Scott, vice president of election services at Associated Press, thank you so much.

DAVID SCOTT: Happy to be here.