Howard Dean doubled down Tuesday on his insinuation that Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE's debate-night sniffles were related to cocaine use.

"That is actually a signature of people who use cocaine," Dean said on MSNBC.

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"I'm not suggesting that Trump does, but I'm suggesting we think about it, because here's the interesting constellation — he sniffs during the presentation, which is something that users do. He also has grandiosity, which is something that accompanies that problem. ... It's something I think it'd be interesting to ask him and see if he ever had a problem with that."

There is no evidence that Trump, the Republican presidential nominee, has ever used cocaine. The businessman has long said he doesn’t drink alcohol or take any illegal drugs.

Dean, a doctor and former chairman of the Democratic National Committee, first raised the cocaine allegation in a tweet on Monday night as social media exploded with commentary about Trump’s breathing, which was picked up by his microphone.

"Notice Trump sniffling all the time. Coke user?" Dean tweeted.

MSNBC's Kate Snow pushed back on Dean's assertions, questioning how they were different from unfounded innuendo about Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE's health from Trump's orbit. Dean countered by criticizing Trump for not releasing "meaningful" health records.

"I raised the question last night," Dean said.

"But I don't think this is a ridiculous idea. Something funny was going on with Trump last night. Do I think it's cocaine, probably not. But again, the sniffling, the grandiosity, the delusions, the pressured speech — this guy has already proven himself to be unstable, the question is: Why is he unstable?

"Do I think he has a cocaine habit? I think it's unlikely that you could mount a presidential campaign at 70 years old with a cocaine habit, but it was pretty striking."