WASHINGTON, United States (AFP) — US President Donald Trump demanded yesterday that his Democratic rival Joe Biden take a drug test for their first debate, which will bring them face to face for the first time in the volatile US presidential campaign.

Tuesday’s clash, coming as Biden leads the charge against Trump’s bid to install conservative Amy Coney Barrett in the late Ruth Bader Ginsburg’s lifetime seat on the Supreme Coart, will thrust the nail-biting contest into a fierce new stage.

For the first time, millions of Americans will watch as the two antagonists — who depict each other as existential threats to the country — step into the ring live on television, after months of shadow-boxing.

Trump, lagging in the polls, taunted Biden yesterday with the fresh 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,” he tweeted, saying he would 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.

When asked by reporters about the demand yesterday, Biden laughed before declining to comment.

Both septuagenarians are prone to blunders and gaffes when speaking — but the 74-year-old Trump has repeatedly depicted the 77-year-old Biden as mentally unfit.

Biden has shrugged off such accusations.