We have our first glimpse of an answer Monday night. Here's a photo of people lining up at a Democratic caucus site on campus at Iowa State University in Story County, a student-heavy area that Sanders has to win if he wants to win the first-in-the-nation voting contest:

Of course, we don't know for sure who these people will vote for.

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And it's worth noting that there are heavier-than-expected crowds all over Iowa right now. The Iowa State Daily shared this photo of a Republican caucus site at a nearby church being moved to the parking lot because of overflow.

The numbers would seem to bear out what we're seeing: As of 10 p.m. Eastern time, with about half of the precincts reporting, Sanders is up in Story County 55 percent to Clinton's 45 percent. That is on the cusp of being the kind of margin he needs in this area, which favored Barack Obama by double digits in his victorious 2008 campaign.

This is all in the realm of anecdotes, right now. But if Sanders wins -- and right now it's very close statewide -- that photo could be one of the first in this 2016 campaign to begin to answer our biggest question about Sanders's viability: Can he turn enthusiasm into votes?

On Saturday, the Des Moines Register reported Sanders drew his biggest crowd yet at Iowa State University, with a crowd of mostly students standing outside for hours to get in.

It looks like at least some of them showed up on Monday as well. And that's good news for Sanders.