Lt. Gov. Juliana Stratton (D) won Illinois’s marquee Senate primary on Tuesday, defeating two House lawmakers and all but assuring she’ll succeed Sen. Dick Durbin (D-Ill.) in the upper chamber.  Voters in Illinois headed to the polls to weigh in on primary races that underscored Democratic divides, drew significant outside spending, advanced one former lawmaker’s comeback bid and, in Statton’s race, posed a key test…