BIDEN CLAIM: "The idea that we're in a situation that is going to destroy Medicare, this is the guy that the actuary of Medicare said ... if, in fact, he continues to withhold -- his plan to withhold the tax on Social Security, Social Security will be bankrupt by 2023."

FACT CHECK: Biden’s claim is misleading on a number of fronts, but is rooted in an action Trump took and comments he made in August.

Trump signed an executive order in August that temporarily halted the collection of the payroll tax, a tax on wages split by workers and their employers. He subsequently asserted that he would like to permanently eliminate the tax.

In 2019, the tax financed 89% of Social Security. Workers and employers each contribute 6.2% of wages, while self-employed people pay the full 12.4%.

However, following Trump’s signing of the executive order, he has said publicly that he will draw from the government’s “general funds” to cover any lost funding for Social Security, a scenario the actuary accounted for in his response to the group of Democratic senators, telling them that the solvency of the program will be essentially unchanged if Trump follows through and actually proposes legislation akin to his public comments.

But since Trump issued his order, and despite Biden’s claims that Trump put forward a full-fledged “proposal,” Trump and the GOP have not unveiled more detailed legislation on how they would prevent the elimination of the payroll tax from impacting the financial security of Social Security.

In late August, Democratic Sens. Ron Wyden, Bernie Sanders, Chris Van Hollen and Chuck Schumer sent a letter to the chief actuary of the Social Security program asking what the effect of eliminating the payroll tax would be. In response, the chief actuary said he was not aware of any “hypothetical legislation” that had been proposed. In simply responding to the scenario posed by Senate Democrats, he said the Social Security benefit program would be depleted of funds by 2023 if there's no additional stream of funding identified to offset eliminating of the payroll tax.

What Trump has not said thus far is what programs could potentially be impacted by the redirection of funds from the government's general fund, only that he will protect Social Security benefits. The general fund finances the operations of the U.S. government, such as recording "funds received and distributed by the Department of the Treasury," and it "includes assets held by government-sponsored entities like Fannie Mae and the Internal Revenue Service."

-ABC News' John Verhovek

TRUMP'S CLAIM: "And I will tell you that I had something that they gave me, a therapeutic, I guess they would call it, some people could say it was a cure. But I was in for a short period of time and I got better very fast or I wouldn't be here tonight."

FACT CHECK: Trump also repeated something he has said before, praising the antibody treatment he received a "cure."

But as of yet, there is no known "cure" for the novel coronavirus.

The antibody cocktail given to the president -- made by biotech company Regeneron -- is thought to be promising, though still in its experimental phase.

Regeneron's experimental treatment is a cocktail of two synthetic, pharmaceutical versions of what occurs naturally in the body to fight off infection. Late last month, Regeneron published positive, yet preliminary data for its cocktail treatment showing it improved symptoms in patients without severe disease.

While the Food and Drug Administration has not yet authorized it, Trump was granted access to it under "compassionate use," enabling him to get it outside of a clinical trial.

A Regeneron spokesperson confirmed to ABC News that Trump's medical staff reached out to the company for permission to use its monoclonal cocktail, and that it was cleared with the FDA.

-ABC News' Sony Salzman and Sasha Pezenik

TRUMP'S CLAIM: "I want to open the schools. The transmittal rate to the teachers is very small."

FACT CHECK: The Centers for Disease Control and Prevention has updated its guidance to note a "body of evidence is growing" that kids "might play a role in transmission." Still, the role children play in community transmission is not yet fully understood. 

In one recent study, the CDC found transmission is unclear: "Recent evidence suggests that children likely have the same or higher viral loads in their nasopharynx compared with adults and that children can spread the virus effectively in households and camp settings."

Schools haven't been studied as closely because many remain closed and not every school is reporting outbreaks. One concern is that children might be transmitting the virus without exhibiting symptoms, and testing people without symptoms remains limited.

Overall, officials say the lower transmission levels in a community, the less likely schools will spread the virus.

-ABC News' Anne Flaherty

TRUMP'S CLAIM: "We have a vaccine that's coming. It's ready. It's going to be announced within weeks. And it's going to be delivered." ... "Johnson & Johnson is doing very well. Moderna is doing very well. Pfizer is doing very well. And we have numerous others."

FACT CHECK: A COVID-19 vaccine isn't ready right now. But it is true that two companies -- Pfizer and Moderna -- could seek emergency use authorization in November or December.

Like Pfizer and Moderna, Johnson & Johnson's vaccine is also in late-stage studies, but Johnson & Johnson paused its trial earlier this month to investigate an unexplained illness.

As the chief adviser to the government vaccine distribution initiative Operation Warp Speed, Dr. Moncef Slaoui told ABC’s Bob Woodruff this week that if a vaccine is authorized before the end of the year approximately 20 million to 40 million doses of it will be stockpiled and ready for distribution for a limited population. At first, only high priority Americans, like those over 65, will have access, but by the springtime more Americans should have access.

Slaoui said that vaccine trials are going as fast as it’s safe to go, pledging to resign if he felt undue pressure from the White House. Slaoui said that by June 2021, it's possible "everybody" in the United States could have been immunized.

-ABC News' Sony Salzman and Sasha Pezenik

The final topic of the night was climate change with Welker first asking each candidate how he would combat climate change and support job growth at the same time as president. Trump answered first.

"So we have the trillion trees program. We have so many different programs. I do love the environment, but what I want is the cleanest, crystal clear water, the cleanest air," Trump said, taking credit for the country's reduced carbon emission last year.

He went on to slam other counties air-quality and tout the U.S. by comparison.

"Look at China, how filthy it is. Look at Russia. Look at India. It's filthy. The air is filthy. The Paris Accord, I took us out because we were going to have to spend trillions of dollars, and we were treated very unfairly," Trump said, closing his two minutes by saying his administration has done an incredible job "environmentally."

When it was Biden's turn, he pivoted to the existential threat he says global warming poses to humanity and said the U.S. has a moral obligation to "deal with it" -- but said climate change also creates a prime opportunity for new jobs.

"Here's where we have a great opportunity. I was able to get both all the environmental organizations as well as labor, the people worried about jobs, to support my climate plan. Because what it does -- it will create millions of new good-paying jobs," Biden said. "Wall Street firms indicated that my plan -- my plan will, in fact, create 18.6 million jobs, 7 million more than his. This is from Wall Street. And I'll create $1 trillion more in economic growth than his proposal does. Not on climate, just on the economy."

Trump slammed Biden's response, claiming the former vice president's plan would cause a massive economic depression and deeming it a "pipe dream," before raising Biden's stance on fracking.

In the face of Trump's criticisms, Welker asked Biden directly, "Would you rule out banning fracking?"

"I do rule out banning fracking," Biden said. "We need other industries to transition to get to ultimately a complete zero emissions by 2025. What I will do with fracking over time is make sure we can capture the emissions from the fracking, capture the emissions from gas. We can do that and we can do that by investing money. It's a transition to that."

"Excuse me," Trump interrupted. "He was against fracking. He said it. I will show that to you tomorrow."

"Fracking on federal land, I said," Biden responded. "No fracking and/or oil on federal land."