“How the heck does any Republican win office in Cook County?”
They don’t. Politically, Cook County is not that far removed from Soviet Russia.
The poll quoted is showing 47.1% support for Foxx vs 40.6% for O'Brien. 2016 numbers:
| Cook County State's Attorney, General Election, 2016 | ||||
|---|---|---|---|---|
| Party | Candidate | Vote % | Votes | |
| Democratic |  Kim Foxx |
72.06% | 1,459,087 | |
| Republican | Christopher Pfannkuche | 27.94% | 565,671 | |
| Total Votes | 2,024,758 | |||
Gotta wonder if the law and order vote will emerge elsewhere around the country. Trump doesn't need a 25% drop in his Democratic opponent's support vs 2016. The same level of support will do just fine for a Trump victory.