President Trump is calling for drug tests to be administered before his first presidential debate with Democratic nominee Joe Biden next month.

Trump made the demand in an Oval Office interview with the Washington Examiner on Wednesday, saying he noticed a sudden improvement in Biden’s primary debate performance against Sen. Bernie Sanders (I-Vt.) in March. He offered no evidence to support his suggestion that the improvement could have been the result of drugs. 

Biden participated in 11 primary debates, most of which were against a crowded field of other contenders, but the last one was on March 15 against just Sanders.

"Nobody thought that he was even going to win," Trump said. "Because his debate performances were so bad. Frankly, his best performance was against Bernie. We're going to call for a drug test, by the way, because his best performance was against Bernie. It wasn't that he was Winston Churchill because he wasn't, but it was a normal, boring debate. You know, nothing amazing happened. And we are going to call for a drug test because there's no way — you can't do that." 

"I don't know how he could have been so incompetent in his debate performances and then all of a sudden be OK against Bernie," he added when pressed to clarify. "My point is, if you go back and watch some of those numerous debates, he was so bad. He wasn't even coherent. And against Bernie, he was. And we're calling for a drug test." 

The president said he was going off his own observations and did not have any inside knowledge of Biden’s campaign.

"All I can tell you is that I'm pretty good at this stuff," he said. 

Trump and Biden are set to square off for their first debate at Case Western Reserve University in Cleveland on Sept. 29. The president did not say when — or to whom — he would officially make his drug test request. 

The Biden campaign did not immediately respond to a request for comment from The Hill.

The Trump campaign has repeatedly sought to boost questions about Biden’s mental faculties, often highlighting past verbal gaffes. 

Trump's supporters regularly voice confidence that he will be benefit from a side-by-side comparison with the former vice president.