Wallace's first question to both candidates was on the Supreme Court. He asked why Trump believes he is right in confirming a justice before the election and why Biden believes he is right in saying the decision should wait until after Election Day.

"I will tell you very simply, we won the election. Elections have consequences," Trump said. "We have the Senate, we have the White House and we have a phenomenal nominee respected by all top top academic good in every way, good in every way."

"And by the way, the Democrats, they wouldn't even think about not doing it if they have -- the only difference is to try and do it faster. There's no way they would give it up. They had Merrick Garland, but the problem is they didn't have the election so they were stopped."

When the question was given to Biden, he said that the American people have a right to say who the Supreme Court nominee should be and that that nomination should wait until the November election concludes as Americans have already begun voting.

"It's just not appropriate to do this before this election," Biden said. "Roe v. Wade and the Affordable Care Act could both be struck down by a conservative Supreme Court."

Multiple Senate Democrats are refusing to meet with Trump's nominee, Amy Coney Barrett, citing the impending election, and have expressed mounting concern with her stance on health care as the Supreme Court is set to hear arguments on the fate of the Affordable Care Act one week after the election.

Senate Republicans, meanwhile, are moving ahead with the nomination despite claims they made in 2016 about not confirming Garland during an election year.

The first presidential debate of 2020 between Trump and Biden kicked off from Case Western Reserve University and the Cleveland Clinic in Ohio with moderator Chris Wallace of Fox News.

Trump and Biden skipped a handshake, customary at the top of such events, due to the coronavirus precautions. Each walked out to his respective lectern without masks.

The candidates will not deliver opening statements. Instead, the debate has been divided into six roughly 15-minute segments on the following topics selected by Wallace: Trump's and Biden's records, the Supreme Court, COVID-19, the economy, race and violence in U.S. cities, and the integrity of the election.

The entire audience -- already limited in its size -- has been tested for COVID-19.

ABC News Chief Anchor George Stephanopoulos said the main question is whether the candidates will do anything in this debate to change the course of this race.

Editor-in-Chief of FiveThirtyEight Nate Silver said that this presidential race is a "much less close race than it was four years ago."

Biden deputy campaign manager Kate Bedingfield fired back at Donald Trump Jr. -- who did an interview with ABC News ahead of her -- saying the president's son continues to deliver personal attacks on the vice president instead of making the case for why Trump should be reelected.

"I was listening to Don Jr. and I didn't hear a whole lot of reasons to vote for Donald Trump," Bedingfield said. "I heard a lot of attacks. I heard a lot of personal criticisms of Joe Biden's son. I didn't hear a whole lot of reason -- if I'm a voter sitting tonight, listening to this debate -- I didn't hear a lot of reasons to vote for Donald Trump."

Bedingfield said Biden will offer a different choice for voters of a leader focused on the issues, not on attacks, and she said success for the evening will be defined by Biden's ability to connect with "families at their kitchen table."

"He's going to be laying out a concrete vision to make life better for people across this country and I think that the clear contrast between somebody who views the world through the lens of having grown up in Scranton, Pennsylvania, versus somebody who views the world through the lens of Park Avenue is going to be very apparent on the stage tonight," she added.

BIDEN'S CLAIM: Biden says 100 million Americans have pre-existing conditions, Trump says he's wrong

FACT CHECK: 100 million or more people have pre-existing conditions in the U.S.

Biden said during the debate that "100 million people" have pre-existing conditions, while Trump said that number was "totally wrong."

"There aren't 100 million people with pre-existing conditions," Trump said. The two candidates were debating about the path forward for health care in America.

Biden, who was arguing that Trump and Republicans would kick people with pre-existing conditions off of health care if they rescinded the Affordable Care Act, is correct that somewhere around 100 million Americans have pre-existing conditions, according to studies.

One study by the Health and Human Services Department in 2017 found that a large percentage of non-elderly Americans have pre-existing health conditions, ranging from 61 million to 133 million.

The study found that "at least 23 percent of Americans (61 million people) using a narrow definition based on eligibility criteria for pre-ACA state high-risk pools, or as many as 51 percent (133 million people) using a broader definition closer to the underwriting criteria used by insurers prior to the ACA" could have been denied health care or offered it at a high price before the Affordable Care Act passed because of pre-existing conditions. The study was published under the Obama administration.

There is a difference, however, between the absolute number of people with pre-existing conditions and the number of people who would be denied coverage under the Affordable Care Act. Experts point out that 54 million non-elderly Americans would've been denied insurance before the ACA, but confirmed that 100 million or more Americans have pre-existing conditions.

"54 million non-elderly adults have a pre-existing condition that would have led to a denial of insurance before the ACA. 100 million or more have a pre-existing condition that would have led to higher premiums or limited benefits," tweeted Larry Levitt, executive vice president for health policy at the Kaiser Family Foundation, referring to a study by the organization.