ILLINOIS — Illinois Republican Gov. Bruce Rauner and billionaire Democratic businessman J.B. Pritzker spent millions attacking each other even before their 2018 matchup was set.

It was just a preview of how brutal and astronomically expensive the race for the state’s top job is expected to be. Rauner is considered one of the nation’s most vulnerable GOP incumbents up for re-election this fall, making the typically Democratic-leaning state a top target.