Before Mayor Rahm Emanuel chose political retirement over the uphill battle for a third term, his annual financial analysis forecast a $97.9 million shortfall for 2019, the city’s smallest since 2008.

Now that Emanuel is a lame duck, City Hall is filling in the blanks in a way likely to double the size of the gap in what will be his eighth and final city budget.

Budget documents distributed to aldermen during closed-door briefings this week include several new obligations that will have to be funded during 2019 — which is now an election year for almost everyone except Emanuel.

There’s an $18 million increase for the Chicago Board of Election Commissioners to cover the cost of the mayoral and aldermanic elections.

There’s a $17.7 million increase in debt service even as Emanuel has yet to decide whether to forge ahead with a controversial $10 billion pension borrowing.

The documents distributed to aldermen also included two more line items: One for “consent decree investments,” the other for “collective bargaining agreement increases.” Neither included a specific cost estimate.

Contracts with Chicago Police officers and firefighters expired June 30, 2017. The Fraternal Order of Police has accused Emanuel of dragging his feet on negotiations and “turning his back” on the rank-and-file.

Former Police Board President-turned mayoral candidate Lori Lightfoot has pegged the cost of implementing the consent decree at $100 million over the next decade.

Nine teams vying for the right to become the federal monitor riding herd over police reform have proposed five-year budgets ranging from $6.7 million to $20 million — and that doesn’t include the formidable costs that must be incurred on the city’s end.

The bottom line: a shortfall pegged at $97.9 million in late July is probably more like $200 million.

No wonder Emanuel’s budget team once again solicited revenue-raising and cost-cutting ideas from aldermen without showing the hand of a mayor who now has a lot less juice to get things done.

Emanuel’s communications director Adam Collins insisted that the added costs can and will be absorbed without forcing the mayor’s City Council allies to walk the tax plank once again.

“There are no tax increases in the upcoming budget,” Collins wrote in an email.

“The mayor has spent the past seven and a half years improving the city’s finances and reducing the city’s structural budget gap. As a result, he has made historic investments in Chicago’s youth. Taxes won’t go up in the Mayor’s budget. Investments in our youth will.”

Emanuel has already imposed a $2 billion avalanche of tax increases, just to begin to solve Chicago’s $28 billion pension crisis.

Chicago taxpayers have endured a parade of property tax increases for police, fire and teacher pensions; two increases in the monthly tax tacked on to telephone bills; and a 29.5 percent surcharge on water and sewer bills.

More tax increases are on the way, but not until after the 2019 mayoral election, when Emanuel will be long gone.

That’s when the five-year ramp to actuarial funding will end and taxpayers will be on the hook to keep city employee pension funds on the road to 90 percent funding.

By 2023, the city’s contribution to all four funds will nearly double – from $1.2 billion this year to $2.1 billion, according to the city’s annual financial analysis.

The $10 billion pension borrowing is intended to minimize the need for another punishing round of post-election tax increases.

But it’s not at all clear that Emanuel still has the clout to get it done at a time when aldermen have been emboldened by his lame-duck status.

Days before pulling the plug on his re-election bid, Emanuel offered a spirited defense of the pension borrowing plan that would, mayoral candidate Paul Vallas has warned, force Chicago taxpayers to wear a “financial straightjacket.”

“I’ve asked my staff to explore all options to achieve the goals of retirement security without overburdening our taxpayers. It would be equally reckless not to explore options … to avoid a significant tax increase when you can minimize that and shore up peoples’ pensions. If we didn’t do that, we wouldn’t be doing our jobs,” Emanuel said then.

“I’ve asked everybody to … think creatively out of the box. One of the things I won’t do is kick the can down the road. … I didn’t create this problem. … I’m … trying to figure out, how do you ensure people’s retirement, which was not done before. And how do we ensure that we don’t let the cost explode to taxpayers. We’ve had a lot of irresponsible decisions made. The responsible thing is to explore options that achieve both goals.”