A Wisconsin Democrat won a State Senate seat on Tuesday night that had been held by a Republican for 17 years, setting off a flurry of political predictions across a state that President Trump won. Republicans warned that it was a “wake up” call for their party as elections loom in the fall, while Democrats cheered the upset victory as a sign of hope that Wisconsin was back in contention. In the state’s first special election of 2018, Patty Schachtner, a Democrat and the St. Croix County medical examiner, beat Representative Adam Jarchow, a Republican member of the State Assembly,...