The volatile U.S. presidential election enters a fierce new stage this week when Donald Trump and Joe Biden hold their first debate, a television spectacle finally allowing Americans to witness the two antagonists head to head.

Tuesday's clash, coming right after Trump defied Democrats and nominated a conservative to replace the late Supreme Court liberal icon Ruth Bader Ginsburg, could again upend an already nail-biting contest.

Biden, 77, leads in polls against the Republican incumbent, both nationwide and in most of the crucial swing states set to provide the decisive electoral college count on Nov. 3. But Trump, 74, is campaigning hard, criss-crossing those battlegrounds on Air Force One while Biden runs a far lower profile strategy. And with his history of skillful showmanship and brutal debate tactics, Trump is hoping the meeting in Cleveland will put him back on top.

Because of COVID-19 restrictions this has been a mostly long-distance election season. That puts even more weight on the first of three 90-minute debates, where tens of millions of Americans will weigh up two men who each accuses the other of posing an existential threat to the United States.

Trump sees his nomination of Amy Coney Barrett to the Supreme Court, potentially tilting the court to the right for years, as a fundamental boost to his troubled reelection campaign. But the live TV debate will be a wild card.

Trump needs to break through the bad news of 200,000 coronavirus deaths, the long-lasting economic fallout and fatigue among swaths of the country at the constant scandal and upheaval roiling his administration. And he has huge confidence in his prowess on stage. Yet unlike the fawning treatment he enjoys during his weekly call-ins to Fox News or the adoring atmosphere at rallies, he'll find himself facing a man painting him as "toxic" in front of the entire country.

"When Joe Biden walks onto the debate stage, it will be the first moment in four years where an American has the opportunity to confront Donald Trump for what he's done," Steve Schmidt, a Republican strategist turned outspoken Trump opponent, said on MSNBC.

Biden, as the front-runner, mainly needs just to keep steady. But he'll be up against a man many would call the best provocateur in the business.

"There is virtually no doubt that Trump will try to bait him," David Barker, director of the Center for Congressional and Presidential Studies at American University, said. "Biden does have a history of being thin-skinned, and most of his most memorable gaffes have come when he is responding to a question or comment that has gotten under his skin."

Trump has spent months denigrating Biden's mental state. He says the former vice president is "shot." He questions whether Biden took drugs to boost his performance during the Democratic primaries. Biden, though, has been through the crucible of the Democratic primary debates earlier this year. He's also been making a string of generally well-received speeches on the campaign trail.

Trump comes with his own weaknesses. Although he often takes questions from groups of journalists, it's rare that he'll do the more risky one-on-one televised session with a tough interviewer. Neither has he had to debate an opponent face-to-face since Hillary Clinton back in 2016. In the days leading up to the Cleveland clash, the Trump campaign has been busily trying to reset expectations, suddenly painting Biden as a master performer.