President Donald Trump has claimed that his Democratic opponent Joe Biden has taken drugs to improve his performance in debates.

Early on, when there were multiple Democratic candidates lined up on stage, Biden was “a disaster” and “grossly incompetent,” Trump said. But at a later debate where Biden was one-on-one with leftist rival Bernie Sanders, “he was OK.”

Trump repeated his demand that Biden should undergo a drug test before their first of three presidential debates scheduled for September 29. “I would take one too,” he said.

Trump has for months tried to persuade voters that Biden is suffering from mental decline.

Reacting to the claims, Biden called Trump ‘fool’, in an interview. “He’s a fool. The comments were just foolish,” Biden said in an interview with NBC affiliate WFLA of Tampa.

Trump made similar unfounded claims about Hillary Clinton during the 2016 presidential election, when he unsuccessfully challenged her to take a drug test, too, because “I don’t know what’s going on with her.”