Former President Trump called on President Biden to take a drug test ahead of Thursday's presidential debate, noting he will also take one.

"DRUG TEST FOR CROOKED JOE BIDEN??? I WOULD, ALSO, IMMEDIATELY AGREE TO ONE!!!" Trump wrote Monday on Truth Social.

The former president and his allies have repeatedly suggested the baseless claim Biden might take a performance enhancing drug before the debate, with some already discounting any well-received performance by the incumbent as a charade. Neither Trump nor others have provided any factual evidence to back up these claims. 

In two other posts on Truth Social, Trump applauded Rep. Ronny Jackson (R-Texas), who sent a letter to the president and his physician Monday, demanding he take drug tests immediately before and after the debate.

"Ronny Jackson was a brilliant Doctor, Admiral and now, a GREAT Congressman," the presumptive GOP nominee wrote in one post. "He happens to be totally right about what is written in this MUST READ Article but, unfortunately, nothing will be done about it!"

The former president and his allies have frequently attempted to characterize Biden as an old, feeble man unfit to serve a second term. They made the drug allegation earlier this year in an attempt to downplay Biden's State of the Union speech, which was generally well-received.

The Biden campaign slammed Trump's allegations on Tuesday. 

 “Donald Trump is so scared of being held accountable for his toxic agenda of attacking reproductive freedom and cutting Social Security that he and his allies are resorting to desperate, obviously false lies," a campaign spokesperson told The Hill. 

When asked about the earlier claims,  Biden-Harris Campaign National Advisory Board Member Mayor Mitch Landrieu called them "trash talk." 

"Trump's going to talk trash like that all the time because that's what he does. The other day you may remember he was trying to question our president's mental acuity and he could not remember the name of his own doctor so tell President Trump, bring whatever he's got, President Biden will be standing there, ready for him," Landrieu told CNN on Sunday. 

Trump and Biden will square off Thursday night in a debate hosted by CNN, in what will be the first presidential debate of this year's cycle. It will be just the two candidates on stage, after other White Hope hopefuls — including independent candidate Robert F. Kennedy Jr. — did not meet the debate requirements.

The debate is widely expected to be a pivotal moment for them as they try to secure votes in the final stretch of the race. Biden, 81, and Trump, 78, both face concerns over their fitness for office, from issues related to their age and temperament.

Biden and Trump are heading into the debate neck and neck in the polls. Trump currently has a slight 1.6 percentage point lead over Biden, per a national polling index by The Hill/Decision Desk HQ.

Trump last week said he does not want to underestimate Biden ahead of the debate.

“Well, all I can say is this: I watched him with Paul Ryan, and he destroyed Paul Ryan,” Trump said during an episode of the “All-In podcast" last week. “And he beat Paul Ryan, so, I’m not underestimating him.”

Biden faced former Speaker Paul Ryan (R-Wis.) in the 2012 vice presidential debate ahead of serving alongside former President Obama. Biden was largely thought to be the dominant figure in the debate.

Updated at 10:27 a.m. EDT