NASHVILLE, Tenn. (AP) — President Donald Trump and Democratic challenger Joe Biden squared off Thursday night in their final debate, which stood as the trailing incumbent’s best chance to change the race’s trajectory with just 12 days until the election.

The Nashville debate offered them a final national stage to outline starkly different visions for a country in the grips of a surging pandemic that has killed more than 225,000 Americans and cost millions of jobs.

The night opened with a clash over the president's handling of the pandemic, which polling suggests is the campaign's defining issue for voters, with Biden declaring, “Anyone responsible for that many deaths should not remain president of the United States of America.”

Trump defended his management of the nation's most deadly health crisis in a century, dismissing Biden's warning that the nation had a “dark winter ahead" due to spikes in infections. And he promised that a vaccine would be ready in weeks.

“It will go away,” said Trump, staying with his optimistic assessment of the pandemic. “We’re rounding the turn. We’re rounding the corner. It’s going away.”

Despite historic tumult, the race has remained largely unchanged with Biden holding advantages in many battleground states while Trump faces a shortage of campaign cash and, crucially, time.

Worried that Trump could lose the White House and cost Republicans the Senate, some advisers urged him to trade his aggressive demeanor from the first debate for a lower-key style and put the spotlight on Biden, whom he derides as “Sleepy Joe.” But Trump made no such promise.

Biden, who has stepped off the campaign trail for several days in favor of debate prep, expected Trump to get intensely personal. Trump's focus on the Biden family in recent days appeared to come at the expense of his last significant opportunity to offer a unifying message to a nation reeling from a virus that killed more than 1,000 people on the day the two men faced off.

The former vice president and his inner circle see the president’s approach chiefly as an effort to distract from the coronavirus, its economic fallout and other crises of Trump's term.

Final debates often play an outsized role in electoral outcomes. But Thursday night's showdown was different from those past.

More than 47 million people have already cast their ballots as part of a pandemic-era rise in early voting. In an election dominated by a polarizing president, far fewer undecided voters remain than at this point in 2016.

In a visual reminder of the pandemic that has rewritten the norms of American society and fundamentally changed the campaign, sheets of plexiglass had been installed onstage Wednesday between the two men. But in the hours before the debate, they were removed.

The debate, moderated by NBC’s Kristen Welker, was a final chance for each man to make his case to a television audience of tens of millions of voters. And questions swirled beforehand as to how Trump, whose hectoring performance at the first debate was viewed by aides as a mistake that turned off viewers, would perform amid a stretch of the campaign in which he has taken angry aim at the news media and unleashed deeply personal attacks on Biden and his adult son.

In an effort to curtail interruptions this time, the Commission on Presidential Debates announced that Trump and Biden would each have his microphone cut off while his rival delivered an opening two-minute answer to each of six debate topics.

The mute button won’t figure in the open discussion portion of the debate.

When he feels cornered, Trump has often lashed out, going as negative as possible. In one stunning moment during the 2016 campaign, in an effort to deflect from the release of the Access Hollywood tape in which he is heard boasting about groping women, Trump held a press conference just before a debate with Hillary Clinton during which he appeared with women who had accused Bill Clinton of sexual assault. He then invited them to watch as audience members.

In a similar move, Trump's campaign held another surprise pre-debate news conference, this time featuring Tony Bobulinski, a man who said he was Hunter Biden's former business partner and made unproven allegations that the vice president's son consulted with his father on China-related business dealings.

Trump — who has urged Attorney General William Barr to investigate the Bidens — has been promoting an unconfirmed New York Post report from last week that cites an email in which an official from the Ukrainian gas company Burisma apparently thanks Hunter Biden, who served on the company’s board, for arranging for him to meet Joe Biden during a 2015 visit to Washington. The Biden campaign has rejected Trump’s assertion of wrongdoing and Biden has denied having anything to do with his son's business dealings.

The final debate was their second, and final, after one slated last week was cancelled. After Trump’s COVID-19 diagnosis, the debate commission switched the would-be showdown to a remote debate. But after Trump balked, the event was scuttled, and the two candidates instead held dueling town halls 1,000 miles apart.

Both men said they tested negative for the virus on Thursday and everyone in the audience wore masks, including First Lady Melania Trump who removed hers during the first debate. Biden took the stage wearing a mask, which he took off as he approached the podium.

Trump did not.

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Lemire reported from Washington, Price from Las Vegas. Additional reporting from Steve Peoples in Nashville, Bill Barrow in Atlanta, Alexandra Jaffe, Stephen Braun and Zeke Miller in Washington and Aamer Madhani in Chicago.