Illinois Gov. JB Pritzker waited until late Friday afternoon to lower the fiscal boom on Chicago.

The governor’s signing of legislation generously sweetening pension benefits for Chicago police and firefighters hired after 2010 was perhaps the worst decision he’s made in his seven years in office.

With the stroke of a pen, Pritzker added more than $11 billion in liabilities to Chicago’s badly underfunded police and fire pension funds. Before the governor’s action, the funds held 25% of the assets needed to meet current and future obligations, which made them two of the most distressed municipal pension funds in the country. That was before this reckless statute.

They now hold 18%. There’s far more reason to worry the money won’t be there when those first responders retire decades from now.

In the days leading up to his signature, Pritzker openly acknowledged fears that the city of Chicago wouldn’t be able to afford the changes. His words raised hopes that he would summon the courage to do his part to help the city right its fiscal ship by vetoing the measure and working to convince lawmakers to uphold the veto, despite the fact that it passed both chambers unanimously. Those votes had taken place before the city performed an actuarial analysis, which later showed how financially damaging the measure would be.

Now was a time for leadership — an act that could have burnished the resume of a governor with national aspirations who’s made real progress improving Illinois’ fiscal standing. Instead, Pritzker shrank from the moment.

Pritzker’s lack of political courage comes with a political price. In a statement on this most costly of unfunded mandates, a Pritzker spokesman said weakly, “The Governor remains committed to maintaining fiscal responsibility at all levels of government and expects the city of Chicago to implement these changes with careful planning and fiscal discipline.”

Careful planning? Fiscal discipline? This is a city facing a $1 billion-plus deficit next year and yawning deficits thereafter. All Pritzker did was make that daunting effort substantially harder. All he did was raise future taxes on Chicagoans.

This act is so irresponsible that there’s rampant speculation its enactment alone could lead the city’s credit rating to be downgraded for a second time this year. If so, that downgrade will be owned by the governor.

Since Mayor Brandon Johnson took office more than two years ago, confidence in the future of Chicago among business and civic leaders has been shaken badly. Pritzker had positioned himself as a check on the mayor’s worst impulses and the voice of fiscal and economic reason in a state and city badly needing adult supervision.

He has functioned that way, too.

He did not do so on Friday.

As the dog days of August arrived, Pritzker took his own political ownership of the fiscal basket case that is the city of Chicago.

Submit a letter, of no more than 400 words, to the editor here or email letters@chicagotribune.com.