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To win the presidency, candidates have to hit the magic number of 270 electoral votes. The Electoral College comprises a total of 538 members, with each state getting a total number of electoral votes equal to its congressional delegation and three additional electoral votes for District of Columbia.

American foreign policy for over half a century was defined by its bipartisan nature, symbolized in the old adage that politics stopped at the water's edge.

But in recent years, foreign policy has become as politically charged as virtually everything else in American life, and when voters mail in their ballots or go to the polls, they'll face a stark difference between the Republican and Democratic nominee and their views of the world and the United States' place in it.

Ahead of Thursday's debate, the Trump campaign made an eleventh-hour demand that the questions focus on foreign policy, as opposed to the topics chosen by the moderator, though the campaigns agreed months ago to allowing the moderator to choose the debate topics.

Read about how Trump and Biden differ on major foreign policy issues including relations with China, Iran, North Korea and NATO allies, among others, here.

-ABC News’ Conor Finnegan

Aides to Trump and Biden separately reported their candidates tested negative for COVID-19 ahead of the final debate.

Earlier Thursday, White House press secretary Kayleigh McEnany told reporters that Trump had tested negative, and Trump’s chief of staff Mark Meadows said the president was tested during the flight from the Washington, D.C., area to Nashville.

They did not offer information on whether the people who accompanied Trump to Nashville -- including Ivanka Trump, Jared Kushner, Tiffany Trump, Bill Stepien, David Bossie and Robert O’Brien -- were tested.

At a NBC News town hall last week, Trump claimed he didn’t remember whether he’d been tested on the day of the first debate, which took place before his first positive COVID-19 test was reported.

-ABC News' Molly Nagle and Jordyn Phelps

Atlanta Mayor Keisha Lance Bottoms tweeted Thursday that she will be attending the presidential debate as a guest of Biden. Bottoms also tweeted that she was a guest at the first debate in September.

Other guests of the former vice president include small business owners Zweli and Leonardo Williams of Durham, North Carolina. Biden campaign senior adviser Symone Sanders said the campaign invited them to draw attention to the struggles of small business owners.

“These small business owners from Durham -- because these are much like small business owners from Wisconsin, like the small business owners down in Georgia, like small business owners all over this country -- who are grappling with how to make ends meet, how to continue to provide, not only for their families but their employees. They're making decisions that, frankly, they shouldn't have to make because the president failed them,” Sanders said.

-ABC News’ John Verhovek and Beatrice Peterson.

TRUMP'S CLAIM: "The children are brought here by coyotes and lots of bad people, cartels, and they're brought here and they used to use them to get into our country." // "They built cages. You know, they used to say I built the cages." // "They are so well taken care of. They are in facilities that are so clean."

FACT CHECK: Trump was defending his now-defunct policy known as "zero tolerance" that required every adult who crossed the border illegally -- even those traveling with their children -- be detained in a bid to deter border crossings.

The result was that thousands of children were separated from their parents in a matter of weeks. It was a major departure from past U.S. policy. In the Barack Obama and George W. Bush administrations, families were separated in rare instances, such as cases of serious crimes like drug trafficking. 

Critics of Trump's policy questioned the conditions the kids were kept in initially at border stations after several died of the flu.

An internal investigation later found that the administration struggled to keep track of the parents, many of whom had been deported. The White House says the parents were contacted and abandoned the children, who were placed with U.S. sponsors, usually family members. The American Civil Liberties Union countered that parents have not been found and contacted and therefore could not give up rights to their children.

Homeland security officials have said that "coyotes" are often used to transport the families for a fee. But there has not been widespread evidence of cases of people falsely presenting themselves as related, with border patrol documenting them as "family units."

Trump's suggestion that "cages" were built by the Obama administration is correct. Obama had faced an influx of children both traveling alone and with families as a result of violence in Central America. And at one point, the Obama administration tried housing the families in special detention centers.

But after a federal judge in California ruled that the arrangement violated a long-standing agreement barring kids from jail-like settings for extended periods, even with their parents, the government began releasing families into the U.S. pending notification of their next court date.

In 2018, photos taken by The Associated Press and posted online by liberal activists suggested the children in steel fencing was Trump's doing. The photos were actually from 2014 when immigration detentions became flooded with families.

-ABC News' Anne Flaherty