When the U.S. Supreme Court in late June declared gerrymandering is a political issue, not one for the courts, all eyes in Illinois turned to Gov. J.B. Pritzker.

Consider for a moment that, in a state with functional politics, the eyes would have been directed at House Speaker Mike Madigan. The longest-serving state speaker in U.S. history, Madigan after the 2020 census will essentially control the drawing of Illinois’ next legislative map. He’ll need to take into account input from Senate President John Cullerton, true. But Madigan will dominate the process in part because of his control over Democratic Party politics, too.

The fact is that no one who understands Illinois politics expects a fair outcome from a Madigan-mandated electoral map. And that’s why our attention inevitably will turn to Pritzker.

At the end of the redistricting process, Pritzker will be the one politician in the state who actually could prevent a gerry-Madiganed map from becoming Illinois law. Sometime in 2021, Pritzker alone will have the power to refuse to sign the bill proposing the new electoral districts.

Were Pritzker to refuse to sign, it would kick off a messy political battle, with high stakes, so his decision is more than just a formality. It actually could mean something—in the hands of a governor who is willing to spend political capital for the good of the state.

Pritzker so far has talked a good game. He has promised to veto an “unfair” map. But what exactly does the governor mean by this pledge? In his eyes, what are the characteristics of a “fair” map? And what specific shortcomings might prevent him from approving one drawn by the state Legislature?

So far, Pritzker has refused to say. And his spokeswoman declines to provide any comment in response to my request for further information.

Let’s not make any assumptions here. At least two years will pass before Pritzker will need to decide whether Illinois’ next electoral map fairly represents the will of the people. There is plenty of time for him to describe in detail just what kind of mapping mischief might prompt him to exercise his veto.

Early in his term, Pritzker has shown a propensity for called shots. He demanded that lawmakers clear the way for a progressive income tax, and they did. He asked for legalized marijuana and got it. Same goes for sports gambling. And his initial $41 billion infrastructure plan actually turned into a $45 billion statewide construction spree.

The time is right for the governor to build on that momentum and declare just what sort of map he won’t abide. In fact, he can send clear directives now, when they can do the most good, about the kind of distortive mapping he won’t allow.

Law and custom define the basic characteristics of a fair map. They should be contiguous and compact in shape. They must protect the representation of minorities and preserve other “communities of interest.” They can observe political subdivisions, such as county or city boundaries.

And what does an unfair map look like? According to the Campaign Legal Center, those characteristics include “cracking,” the practice of parceling a targeted group into several districts to prevent it from achieving a majority in any one of them. “Hijacking” is when incumbents are moved out of their districts, and “kidnapping” when two incumbents are forced into a single district.

“Packing” happens when a group’s numbers are concentrated in ways designed to give it majorities in the fewest possible districts. “Stacking” is when a racial or other group is concentrated in one district, but just short of the numbers needed to win. Then there is “tacking,” when a concentrated number of people are added to a district, with an eye toward tipping the electoral balance in a group’s favor.

Does Pritzker disapprove of all these techniques? Are there others he’ll be keeping his eye on, too?

Those are questions the governor should answer now, before the details of political mapmaking begin to take shape after the 2020 census. Gov. Pat Quinn made essentially the same promise as Pritzker and wound up approving a gerrymandered map in 2011.

If Pritzker is serious about defending representative government in Illinois, he will use the time between now and 2021 to offer his definition of an “unfair” map. He’ll be prepared to use his veto and politic behind the scenes early to guard against an override by a Madigan-led supermajority.

The Supreme Court declared gerrymandering a political problem, not a judicial one. Pritzker can bring justice back into the Illinois process—and reduce the chances of a gerry-Madiganed outcome—by defining a fair map now.