“I sometimes wonder whether people actually understood the math,” says Peter Chan, former head of the U.S. Securities and Exchange Commission's municipal securities and public pensions unit in Chicago.

At worst, policymakers deliberately ignored the warning signs, punted the problem far into the future and habitually enjoyed the short-term gratification of funneling more money into schools and other operational needs instead of pensions.

“They took basically the path of least resistance. If we don't have to pay for it now, let's not,” says Henry Bayer, retired longtime executive director of the American Federation of State County and Municipal Employees Council 31, which represents 36,000 state workers.

The parade of horribles includes:

•Shorting pension payments to buy immediate budgetary relief. The nonpartisan Commission on Government Forecasting and Accountability, the fiscal research arm of the General Assembly, concluded in 2013 that the largest cause of the unfunded pension liabilities was inadequate contributions from the state. Underpayments between 1985 and 2012 totaled $41.2 billion, the agency calculated.

•Enhancing pension benefits. Former GOP Gov. James Thompson agreed in 1989 to establish a compounding, 3 percent cost-of-living increase for retirees. Another round of benefit enhancements followed in the late 1990s. In May, the state Supreme Court ruled that those changes can't ever be revoked for tens of thousands of current and retired government workers.

•Clearing a bloated state payroll by letting workers retire early. A 2002 plan created under Republican Ryan and pushed by Democratic House Speaker Michael Madigan cost the pension systems at least four times more than originally billed and won't be paid off until after 2045, when early-century budgetary ills will be the stuff of history books.

Other factors happened outside policymakers' control. The collapse of the dot-com bubble in the early 2000s and the 2008 stock-market meltdown accounted for a combined $15.9 billion in pension-investment losses, CGFA reported. And an adjustment downward in long-term investment return assumptions in 2011 pushed Illinois' pension systems $9.8 billion deeper into the red.