President Trump says he will call for drug tests for both former Vice President Joe Biden and himself before the first candidates’ debate on Sept. 29. In an Oval Office interview Wednesday, the president expressed suspicion at what he said was a sudden, marked improvement in Biden’s debate performance during the Democratic primary season and suggested that he believes the improvement was the result of drugs. The president offered no evidence to support his speculation.

Biden took part in 11 debates during the primary season. Most were against a crowded field of candidates, but the final debate, on March 15, was just Biden and Sen. Bernie Sanders. The president claimed to see a big difference between the last debate and those that came before.