WASHINGTON - The volatile US 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 conservative Amy Coney Barrett to replace the late Supreme Court liberal icon Ruth Bader Ginsburg, could again upend a nail-biting contest.
Trump, lagging in the polls and with a history of trying to rattle debate opponents, taunted Biden on Sunday with a tweet launching a new salvo on his mental acuity.
"I will be strongly demanding a Drug Test of Sleepy Joe Biden prior to, or after, the Debate on Tuesday night," Trump said. "Naturally, I will agree to take one also. His Debate performances have been record-setting UNEVEN, to put it mildly. Only drugs could have caused this discrepancy???"
The president offered no evidence to support his insinuation, and recently-completed negotiations between the Biden and Trump camps over debate conditions reportedly made no mention of any drug test.
Both septuagenarians are prone to blunders and gaffes when speaking.
But as the 74-year-old Trump has repeatedly depicted the 77-year-old Biden as mentally unfit as he tries to eat away at the Democrat's persistent poll lead.
There was no immediate response from Biden to the Sunday tweet, though the former vice president was set to speak to reporters at 12:15 pm (1615 GMT).
He has shrugged off such accusations from Trump in the past. On Saturday said he expects "personal attacks and lies" from the president, likening Trump to Nazi propaganda chief Joseph Goebbels.
The former vice president has until recently stayed close to his Delaware home due to the challenges of campaigning in person safely during a pandemic.
Trump, meanwhile, has been flouting his own government's social distancing guidelines to speak frequently at mass rallies where participants are often tightly packed with few masks in sight, as he crisscrosses battleground states on Air Force One.
The COVID-19 restrictions place even more weight on Tuesday's 90-minute debate, the first of three, with millions of Americans weighing two men who each depict the other as an existential threat to the country.
Trump sees his nomination of Barrett to the Supreme Court -- potentially tilting the court to the right for years -- as a fundamental boost to his troubled re-election campaign.
He told Fox & Friends Sunday the Senate will "easily" confirm Barrett before the election, despite furious Democratic opposition.
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 widespread fatigue at the constant upheaval roiling his administration.
He sees himself as a tough guy and 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 determined rival 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 frontrunner, mainly needs just to keep steady. But he'll be up against a man many call a master provocateur -- as with the drugs tweet Sunday.
"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."
WHO'S MORE READY?
Trump has spent months denigrating Biden's mental state, saying the former vice president is "shot."
Biden, though, survived the crucible of the Democratic primary debates earlier this year and has made a string of generally well-received speeches on the campaign trail.
And while Trump 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 Clinton in 2016.
"Normally, that first debate is the toughest for the incumbent," said Aaron Kall, director of debate at the University of Michigan and co-author of "Debating The Donald."
The debate moderator, Fox News host Chris Wallace, has set topics ranging across the Supreme Court, he pandemic and economic disasters, racism and the integrity of the election itself.
But whether Wallace can keep the two men on topic remains to be seen.