Update: Dean doubled down on his assertions in an interview with MSNBC on Tuesday, despite absolutely no evidence to prove his point. An updated post follows.

Let's say right off the bat that what Howard Dean, a former presidential candidate and governor of Vermont, suggested in a Tweet Monday night (above) is totally and completely unsubstantiated. Donald Trump says he doesn't even drink alcohol, and no journalist has ever found evidence otherwise.

But from the moment Trump took the stage for the first presidential debate, viewers couldn't help but notice something: He was sniffly. In fact, The Post's Gillian Brockell counted Trump sniffed at least 36 -- wait, 37 -- times during the 90-minute debate. (He also interrupted Clinton 28 times, but that's another story.)

Republican presidential nominee Donald Trump had a case of the sniffles during the first presidential debate on Sept. 26 – so we put them all in one supercut, with a few of his interruptions for good measure. (Gillian Brockell/The Washington Post)

So what's going on? Twitter, of course, had its theories -- among the most colorful was the drug use (when snorted, cocaine can cause nasal drip. Gross, I know).

Dean was among the most prominent to share that (again, totally unsubstantiated) theory. He doubled down on it in an interview Tuesday on MSNBC: "Look, do I think at 70 years old he has a cocaine habit? Probably not, but you know, it's something I think it'd be interesting to ask him and see if he has a problem with that."

Here's some other theories about why Trump was sniffling so much:

The most obvious was that maybe he was under the weather.

Or that he was having trouble breathing.

Or that he has some other kind of sinus problem (Hillary Clinton's recent doctor's letter says she's suffered from sinus problems, too!).

Or, since we've covered all the other medical problems that could cause one to sniffle, why not allergies?

But The Fix's own editor, Rebecca Sinderbrand, has another idea: Sniffling is a tic Trump does when he's on stage. We at The Fix watch a lot of Trump rallies, and Sinderbrand has noticed that Trump often sniffs into the microphone at events:

For what it's worth, it's a tic which becomes especially noticeable when he's reading off a teleprompter or during high-profile events. And Trump has never before participated in an event quite as high-profile as tonight's.