Crowds indicate level of support.
Stop right there, because no they do not. They indicate level of interest which is not the same thing.
If a tractor trailer across the road flips over and bursts into flames --- that draws a crowd too. Doesn't mean that crowd 'supports' the idea of flipping over and bursting into flames.
Again --- nobody in the world needs to go see Donald Rump for the purpose of finding out what he has to say. By now everybody knows too well what he has to say --- they're there to watch the delivery. Because there's a better-than-even chance that you get to witness another meltdown and maybe even a fistfight. They already know there's some ethnic/misogynist slur or some outrageous war fantasy or some juvenile trolling coming --- they just want to witness it happen live. Purely for the feeling of it.
Simply put, people go see Rump for exactly the same reason people watch fake TV wrestling. Again, people go to see freak shows. We've got one candidate who's a freak show and another who isn't. If you're a street vendor --- you go with the freak. That's where the audience is.
And nobody knows this phenomenon better than Rump. He's been playing this card the entire time, and he's obsessed with attention. Think back to his hissyfit about not going to a debate because mean ol' Megyn Kelly would be there, and how he held his own pseudo-event and then huffed "we'll see what the ratings are". Again --- attention. It's his entire obsession.
If rally audiences corresponded to voting support, you'd see Rump pulling 90% (or whatever the contrast is) of the vote total tomorrow.
But you won't. Voting is not going to see a freak show, even if it does have eerily similar results.
Ok. They indicate interest. What does it say when the interest in your candidate is so low that they can't fill a 500 seat room? Or that their running mate can't get more than twelve people to show up to an event? That seems like a reeally, reaally, low level of "interest".