Not unexpected, turnout for the 2012 Democratic caucuses was significantly lower than 2008. The Iowa Democratic Party reports that "more than 25,000" people participated in the 2012 Democratic caucuses, compared to 236,000 in 2008.
What a bizarre factoid to drop in the middle of an unrelated article! "Wow, read this, honey! Democratic turnout in Iowa was way down! I guess there really is a huge enthusiasm gap!"
The point Mr. McDonald forgets to make is that Democrats have no one to caucus for.
It's a non-binding opinion poll with only one name on the ballot. They might as well be voting for which of Earth's moons they like the most.