AP Photo/Carolyn Kaster
Earnest said later that he wasn't accusing Trump of using drugs but was simply "having a little fun."
The press secretary was referring to Trump's repeated apparent sniffling through the first two presidential debates, which set social media ablaze as viewers wondered if it was a nervous tic, a cold, or something else.
Former Vermont Gov. Howard Dean, a 2004 Democratic presidential candidate, tweeted during the first debate that Trump was "sniffing all the time. Coke user?"
Dean later doubled down on the theory in an interview with MSNBC.
"Well, you can't make a diagnosis over the television, but [the sniffling] is a signature of people who use cocaine," Dean said. "I'm just suggesting that we think about it. He sniffed during the presentation, which is something that [cocaine] users do. He also has grandiosity, which is something that accompanies that problem."
Trump called for the pre-debate drug test at a rally in Portsmouth, New Hampshire, on Saturday, suggesting without evidence that Clinton may have been on drugs during the second debate.
"We're like athletes," Trump said. "But athletes, they make them take a drug test, right? I think we should take a drug test prior to the debate."
"We should take a drug test because I don't know what's going on with her," Trump continued as the audience cheered. "Anyway, I'm willing to do it."
Trump said that at the beginning of the last debate, at Washington University in St. Louis, Clinton was "all pumped up," and that by the end she could "barely reach her car."