One of the local TV stations holds an informal poll at the Iowa State Fair called "Cast Your Kernel", where there are jars with each candidate's name on it and a person is given a kernel of corn and drops it into the jar of their choice. Results are tallied and released periodically through the day, typically at each daily newscast.
It's terribly unscientific, because there's not much control - while kids can't "vote", it's not like they're checking ID's for ages, and of course someone could come back back a couple of hours later and probably vote again if they had a mind to with a decent chance they wouldn't be recognized.
It's also of course limited to people attending the Fair who happen to pass the booth on the Concourse and are interested enough to take a moment to vote, and there are no controls on whether one is actually a likely or even a registered voter. And finally, the jars are clear glass, so it's easy to see what candidates are getting the most kernels, which might influence people on their vote ("follow the herd" and vote for the one with the most votes, or be a contrarian and drop a kernel in a jar with only a couple in it). Also, it's not like a private ballot, so a person might drop a kernel for a candidate even if they don't care for them just to keep the peace with the father-in-law watching them vote.
With those caveats in mind, the results from earlier today are below the fold (and a bit more commentary):
Among Democratic Candidates:
Hillary Clinton: 58%
Bernie Sanders: 34%
Martin O'Malley: 6%
Jim Webb & Lincoln Chafee both came in at 1%.
Among Republican Candidates:
Donald Trump: 31%
Ben Carson: 21%
Carly Fiorina: 8%
Jeb Bush, Marco Rubio, & Mike Huckabee: 6% each
Ted Cruz: 5%
Scott Walker: 4%
John Kasich, Rand Paul, & Chris Christie: 2% each
Rick Perry & Rick Santorum: 1% each
Jim Gilmore, Lindsey Graham, & George Pataki: <1%.
Now, having noted all the reasons why this is very unscientific, I think it's still worth noting that this poll puts Trump in the lead and Carson in 2nd place. The CNN/ORC poll of Iowa Republicans released earlier this week likewise put Trump out front with Carson in 2nd (with 22% and 14% of those polled, respectively).
In contrast, though, Walker was 3rd in the CNN poll and is substantially down the list on this one.
I guess a final caveat: Trump was in town today, stumping at the Fair and giving free helicopter rides near the fairgrounds.