WASHINGTON, Oct. 22 (Xinhua) -- U.S. President Donald Trump and former Vice President Joe Biden will meet Thursday night for the final presidential debate, offering voters the last look at the Republican incumbent and his Democratic challenger facing off each other head-to-head less than two weeks before Election Day.

The back-and-forth quarrels between the two campaigns over everything from the debate's governing rules to its schedule have made the process so volatile that it becomes a snapshot of an unorthodox election amid the coronavirus pandemic this year.

After the candidates' first encounter on Sept. 29 that descended into a chaotic shouting match which has rarely been seen in past debates, Trump refused to participate in a virtual showdown arranged due to his infection with the coronavirus, resulting in the second round of debate having been canceled and the candidates holding their own town hall meetings with voters.

While allowing the final debate to be held in-person, the Commission on Presidential Debates -- the nonpartisan organizing body of the event -- made a change to the rules that will mute the candidates' microphones when their opponents are given two minutes to answer the first question of each of the six 15-minute segments, so that the one who is speaking won't be interrupted.

NBC News' White House correspondent Kristen Welker is chosen as moderator for the Thursday night debate. Topics for discussion include "Fighting COVID-19," "American Families," "Race in America," "Climate Change," "National Security" and "Leadership." These issues will cover an uninterrupted 90-minute period beginning at 9:00 p.m. ET.

For Trump, the one-on-one with his rival will be especially crucial in that it is his last opportunity to directly convince what is still expected to be a large number of national audience, thus hopefully overcoming his current deficit in both national and battleground state polls.

Among the hot-button issues Trump must address is his mishandling of the pandemic, which still concerns undecided voters, and which will almost surely continue to dog the president as long as the virus is not brought under control.

There's no reason for Biden to be complacent, though, as his campaign recently warned of the inaccuracy of the polls.

At the upcoming debate, the former vice president is expected to face attacks from Trump for his alleged involvement during the vice presidency in his son Hunter Biden's business in Ukraine. Biden has denied any involvement.

Biden will probably also have to further clarify, whether on the night's occasion or in the following days leading up to Nov. 3, his stance on progressive Democrats' advocacy for expanding the number of justices on the Supreme Court, which would see a 6-3 conservative majority after the all-but-certain Senate confirmation of Judge Amy Coney Barrett, a Trump appointee.

In an interview with CBS "60 Minutes" program to be aired Sunday, Biden said he will set up a commission to study the reform of the high court if elected.