This may hardly be breaking news to you, but politicians don't always say precisely what they think. Sometimes, however, they do—and the fleeting moment between such bursts of frankness and the seemingly inevitable walk-back can be bracing and memorable.

Something like that happened Aug. 30, when Chicago Mayor Lori Lightfoot visited Crain's editorial board the morning after a "State of the City" address, delivered on her 100th day in office, in which she pegged the size of the budget gap she must fill in 2020 at an astonishing $838 million.

During a lively exchange on pensions—the biggest driver of the city's financial hardships, as the cost of paying old pension debt is set to rise almost $1 billion over the next three years—Lightfoot opened a window into her thinking. It was a window her team would later that day hurry to slam shut, but she opened it nevertheless, and Lightfoot is too smart for anyone to believe the lapse was entirely accidental.

First understand, if you didn't already, that one of the biggest drivers of the city's and the state's ballooning public employee pension costs are so-called COLAs—the 3 percent compounded annual increases in pension benefits paid out to many non-police/fire government retirees, even though inflation lately has been running around 1 percent a year. Courts have ruled those COLAs untouchable thanks to a clause in the Illinois Constitution that says pension benefits cannot be "diminished or impaired." Union pensions are, of course, sacred ground for Illinois Democrats. Our new governor, J.B. Pritzker, has certainly trod lightly there, as have other Democratic leaders like former Gov. Pat Quinn and current Senate President John Cullerton, even as they have sought legal means to trade those COLAs for something of similar value—like, say, solvency—only to be swatted back by the courts, leaving no recourse other than a constitutional amendment to unshackle government entities from promises they can no longer afford to keep.

Lightfoot called those COLAs "unsustainable"—out loud, on camera—and let the observation hang there in the air, despite ample opportunity to reframe her words. Though she took pains to add she wasn't advocating for a constitutional amendment to change the COLA formula or any other aspect of public employee pensions—relief only Springfield can deliver—she noted that "I'd like to put as many options as possible on the table." And when later asked whether cost-of-living increases ought to, you know, be tied to the actual cost of living, Lightfoot replied, "What a concept, right?" with a grim chuckle, adding, "I think that's something that we absolutely have to talk about."

Of course, Lightfoot is right to call 3 percent COLAs unsustainable. They might have been tenable had politicians not taken a pass on paying the pension funds what they were owed, sometimes for years at a stretch, even as workers dutifully paid in. And against that backdrop, it's understandable that unions sought and won a guarantee that politicians wouldn't be allowed to borrow against their members' retirement security to pay for government services they weren't brave enough to ask taxpayers to cover. But given the straits all of us—union and nonunion workers alike—are now in, a guaranteed 3 percent annual bump is hard to argue for, particularly in a sustained low-inflation environment.

Half-measures like two-tiered pension plans that offer new hires less than their veteran colleagues enjoy have only gotten us so far. It's increasingly clear casinos and legal marijuana are going to deliver far less revenue than budget optimists had hoped. And borrowing more is prohibitively expensive, particularly given Wall Street's generally dim view of the city's and state's creditworthiness.

The hard truth is Illinois needs a constitutional amendment to fix the pension clause. The mayor may not be willing to say it in so many words, but this is the relief she needs, and the governor, despite his protestations, needs it, too. He must rethink his previously ironclad opposition to a pension amendment. Doing so may guarantee that the unions that helped whisk him to victory in 2018 will do everything in their power to defeat him in the next election. But short of the sort of meaningful pension solution that only a constitutional amendment can deliver, it's fair to wonder whether Pritzker's job will be worth having come 2022.