Trump beat Hillary in Wisconsin in 2016 by just 24,081 votes.
With turnout from 2012 down by 91,000, one could explain Trump's victory by saying Wisconsin Democrats stayed home in enough numbers in 2016 to help elect Trump. And since of the last three presidential elections turnout in Wisconsin was highest in 2012 at 3.068 million when the state helped return the incumbent Democrat to office, the argument possesses considerable plausibility.
Compared with 2008, however, this explanation fails since 2016 turnout undershot 2008 by just 6,000, not enough to account for Trump's victory over Hillary.
Both Iowa and Wisconsin were slow to the trend of turnout peaking in 2008 when the popular Democrat Obama won in an election with still unequaled turnout of 131.5 million nationwide.