Here’s a rundown of the two candidates and the factors that could decide the race, from Tuesday’s POLITICO Illinois Playbook:

How they’d approach crime: Vallas wants to increase the Chicago Police Department by 2,000, while Johnson wants to improve social service programs to address what he sees as the root causes of crime.

What they agree on: They both support keeping Lightfoot’s Invest South/West program for economic development on the Sound and West sides.

Their union labels: Johnson is backed by the liberal Chicago Teachers Union, and Vallas is supported by the conservative Fraternal Order of Police. Vallas has accepted donations from conservative donors, while Johnson’s campaign is backed almost solely by teachers’ unions and organizations.

Their Achilles’ heels: Johnson has been quoted saying he wants to defund the police, though he has since walked back his comments. And Vallas has been critical in the past of high-profile Democrats in his own party.

The problem for moderates: “Voters are making a choice between the conservative status quo like the Richard Daley era, or a progressive in Johnson,” political consultant and former alderman Dick Simpson said. It’s causing some existential angst among voters who might have backed Lightfoot or Rep. Jesus “Chuy” Garcia in the first round of the election.

It’s historic: Simpson says the race is different than most any other mayoral race Chicago has ever seen. “Going back to 1871, there’s been a split between machine candidates and reform candidates. What’s different this time is that the choice is between conservative status quo and progressive.”

Black and white voters: Simpson and other political watchers say the African American vote will be essential for both candidates. Johnson must get 80 percent of the Black vote to win, and Vallas needs above 20 percent for him to make it over the finish line. The numbers are pretty much reversed for white voters.

Latino vote is more complicated: Garcia has backed Johnson, but many Latino voters have aligned with Vallas over his focus on fighting crime.

We may not know tonight who wins. Polls close at 8 p.m. Eastern/7 p.m. Central. Polling is showing the race within the margin of error, which means there may not be clear winner until mail-in ballots are counted. Johnson, for example, went up a few points after the night of the primary thanks to mail-in-ballots, which were tallied later.