The City Council on Wednesday came within one vote of blocking a $3.5 billion O’Hare Airport bond issue, delivering another powerful message about the lack of minority participation on city contracts and the gravy train of pinstripe patronage tied to city borrowings.

For months, aldermen have been pushing back in response to the Laquan McDonald controversy that has politically weakened Mayor Rahm Emanuel.

But never before has legislation championed by the mayor — let alone an ordinance as important as a $3.5 billion O’Hare bond sale — been approved by the bare minimum of 26 votes.

That’s what happened Wednesday. The vote was 26 to 21.

Just one more vote and the Black Caucus would have had enough votes to block a $3.5 billion borrowing that Emanuel plans to use to bankroll his signature plan to build a runway at O’Hare, overhaul the international terminal and a host of other airport projects and cost-saving re-financing.

Four aldermen joined the entire Black Caucus in voting no: Susan Sadlowski Garza (10th); Milly Santiago (31st); Scott Waguespack (32nd) and Deb Mell (33rd).

Wednesday’s narrowest of wins on the O’Hare bond sale was clearly an embarrassment to Emanuel and a show of weakness or, at the very least, vulnerability.

“I don’t see it that way,” the mayor said. “I know you want to see it from the earnestness of the politics. But I’m actually looking at it from the earnestness of the people who spoke up on behalf of minority businesses that are trying to break into the professional area. Which is why I made changes pre- this vote.”

Emanuel said he talked to Aviation Commissioner Ginger Evans over the weekend — after the O’Hare bond sale was held up in committee — and told her that she has “some work to do because I respect the principle of what the aldermen were saying and see that principle and that value.”

Ald. Pat Dowell (3rd), the prime mover behind the effort to block the O’Hare bond issue, said she considers the vote a “message to Evans” — not the mayor.

Black Caucus Chairman Roderick Sawyer (6th) agreed. He called the black contracting numbers at O’Hare “disgusting,” the number of black attorneys on the law firms benefitting from city bond issues “appalling” and the vote a bold departure from the timid protests of the past.

“Year after year, we get these numbers. They’re deplorable. Yet we continue to vote for whatever the initiative may be. Now we’re saying we’re tired of it. We’re not gonna continue to vote for it,” Sawyer said.

Sawyer said the revolt was hatched after weeks of meetings with the Aviation Department.

“It just bubbled out. My colleagues were frustrated and upset with the continuing lack of growth in the numbers, and it just got to a boiling point where we’re just not gonna take it any longer,” he said.

Former Black Caucus Chairman Howard Brookins (21st) agreed that the political message “has never been [delievered] like it was today where this thing almost failed. . . . We need to flip one more person so it will fail.”

The narrow approval came on the same day that Emanuel proposed giving his chief procurement officer sweeping new powers to spread city contracts around instead of letting a handful of heavy-hitters dominate.

The mayor’s ordinance would divide the city into multiple geographic districts for the purpose of awarding city contracts and give the chief procurement officer “sole authority to determine the maximum number of contracts that may be awarded to any single contractor” in those districts.

The mayor’s office said the change was designed to “protect the city from contractors that overextend themselves or find that they are unable to perform work [i.e. go out of business] and the city must issue an emergency procurement.”

The ordinance has the potential to make things difficult for a handful of clout-heavy construction contractors who usually are big enough to under-bid the competition to dominate city business, particularly in black and Hispanic neighborhoods.

The mayor introduced yet another ordinance that would empower Chief Procurement Officer Jamie Rhee to “enter into contracts with more than one vendor for the provision of goods, work or services to address” city emergencies. The dollar limit on that emergency spending, without competitive bidding, would to $250,000 for each contract.

Another ordinance would allow small and medium-sized companies to compete exclusively against each other for city construction contracts of between $3 million and $10 million.

The new program would be “race- and gender-neutral.” But it could be a boon to minority contractors struggling to gain a foothold in the industry.

And yet another ordinance would disqualify from doing business with the city any company that has been “debarred” by another government agency for the duration of that ban.