Moderator Chris Wallace has repeatedly tried to keep Trump from interrupting Biden.

"It's hard to get any word in with this clown," Biden said, "excuse me, this person."

Amid bombshell reporting in the New York Times on the past two decades of Trump's taxes, Wallace put the first question to the president.

"Is it true that you paid $750 in federal income taxes?" Wallace asked.

"I paid millions of dollars in taxes," Trump responded. "Millions of dollars of income tax."

But the president never fully answered if that was federal income tax.

Trump paid just $750 in income taxes in 2016, the year he ran for president, and in 2017, his first year in the White House, according to the Times report.

Biden, meanwhile, paid nearly $288,000 in federal income taxes last year, according to returns he released just hours before his Tuesday night debate, an effort to draw a sharp contrast with the revelations about Trump's tax returns.

Democrats said if the president is upwards of $400 million in debt as the New York Times has reported, he poses a national security threat to the country.

Wallace pressed on, asking "Mr. President, I'm asking you a question. Will you tell us how much you paid in federal income taxes in 2016 and 2017?

"Millions of dollars," Trump replied.

The president then blamed Biden for the tax codes since Biden has worked for so long in Washington.

"I'm going to eliminate the Trump tax cuts," Biden said.

"You are the worst president America has ever had," Biden continued.

"Let me just say, I've done more in 47 months than you've done in 47 years, Joe," Trump replied.

In a heated discussion on tax policy, Biden criticized Trump's trade policies with China which led to the first thinly veiled mention of Hunter Biden on stage.

"He talks about the art of the deal. China's perfected the art of the steal. We have a higher deficit with China now than we did before, we have the highest deficit -- trade deficit with Mexico," Biden said, before Trump interrupted.

"China ate your lunch, Joe. And no wonder your son goes in and he takes out what he takes out, billion of dollars," Trump said, before launching personal attacks on Biden's son, Hunter Biden, and his business dealings while his father was vice president. Hunter Biden has denied any wrongdoing.

"We want to talk about families and ethics? I don't want to do that. I mean his family, we can talk about all night," Biden responded, then said the American people don't want to hear about their families.

Asked about how they would deal with economic recovery, Trump said he would avoid further shutdowns, touted the current economic recovery and credited himself with bringing back college football.

"Our country is coming back incredibly well, setting records as it does it. We don't need somebody to come in and say let's shut it down," Trump said, though Biden said he would not impose a full shutdown as the president suggested.

Biden then took the opportunity to speak directly to American families on Trump's taxes and repeated his mantra that the U.S. "can't fix the economy without fixing COVID."

"The difference is millionaires and billionaires like him in the middle of the COVID crisis have done very well," Biden said. "You folks living in Scranton and Clayton and all the small towns and working-class towns in America: How well are you doing?"

TRUMP'S CLAIM: "And now, we're weeks away from a vaccine."

FACT CHECK: Most prominent public health experts have said that a vaccine will not be widely available until mid 2021.

The pharmaceutical company Pfizer has said they may have data from its late-stage trial by October. Moderna has said it could have data from its late-stage trial by November or December. From there, the data will need to be analyzed by the FDA to determine whether the vaccine is both safe and effective. Other companies in late-stage trials are further behind. AstraZeneca's late stage trial is still on hold, and Johnson and Johnson only just started its late-stage trial this month.

Even if a vaccine is authorized by the end of the year, that does not mean it will be widely available. At first, only limited supplies will be available, and they will be prioritized for the most vulnerable.

"By the time you mobilize the distribution of the vaccinations and you get the majority or more of the population vaccinated and protected, that's likely not going to happen until the mid- or end of 2021," Dr. Anthony Fauci, the nation's top expert on infectious diseases, told MSNBC's Andrea Mitchell earlier this month.

In a recent Senate hearing, CDC Director Robert Redfield echoed those sentiments, "I think there will be vaccine that will initially be available some time between November and December, but very limited supply, and it will have to be prioritized," but, he said, "If you're asking me when is it going to be generally available to the American public so we can begin to take advantage of vaccine to get back to our regular life, I think we're probably looking at late second quarter, third quarter 2021."

-- ABC News' Sony Salzman