From this
CNN article (emphasis is mine):
Voters in Wisconsin just weren't as angry, or frustrated, with Republican leadership as voters in other states. Four in 10 say they're scared about Trump as the nominee. And many said Trump, not the man he has branded "Lyin' Ted," has run the most dishonest campaign.
Coming off perhaps the worst week of his campaign, Trump -- who'd claimed as recently as Tuesday morning that he thought he'd win the Badger State -- fell far short. He split the vote with Cruz of Republicans who said they wanted a candidate who could bring change. He was blown away by those worried about electability.
One especially concerning figure for Trump: He was blown out by 22 percentage points by Cruz in suburban areas and 13 points in urban areas, compared to just 3 points in rural areas. That's bad news as the race moves to the densely-populated east coast.