One of Mike Bloomberg's signal accomplishments in New York City was reversing the flow of corruption. In the old days, and in every other city in the world most days, favor-seekers bribe politicians — with cash in envelopes, with legal contributions, or with political support. In Mike Bloomberg's New York, the mayor bribed you, buying the silence or cooperation of individuals, cultural organizations, and social service groups with hundreds in millions of dollars spent on small personal favors — a legal payment here, a medical procedure there — and charitable contributions.

As a liberal Democrat, Bill de Blasio's biggest challenge when he takes power in January will not be keeping crime down or funding an ambitious expansion of early education. It will be dealing with the explosion of Bloomberg's machine after the grease of money is gone and the gears start sticking.

Bloomberg's wealth, and his generosity, "was protection money. In many ways it inoculated him from potential criticism and stimulated people to do things that they might not have or shouldn't have done," says Doug Muzzio, a professor of public affairs at New York's Baruch College. "Now the pie is smaller and the needs are larger, in the end there's going to be enhanced conflict. And it's going to take place in the halls of City Hall. It's going to be the old days."

Bloomberg's close aides have always acknowledged that his wealth was, as much as his electoral mandate, a central source of power. But many observers confuse this civic grease for the straightforward millions he's spent getting himself elected. The other money has been, for several reasons, hard at times to characterize, a secret lubricant of urban consensus.

That's in part because the participants in the machine — the mayor, and the recipients of his largesse — have a shared interest in not talking about it. (For a time, he actually gave his contributions through the Carnegie Corporation, under a thin veil of anonymity.) It's partly because much of it is endless personal generosity in paying for peoples' medical care, for instance, not ugly quid pro quo influence shopping. And it's partly because the mayor's wealth is wealth on the new scale, wealth that Americans have trouble reckoning with — not Upper East Side society millions, but billions that can be tapped, practically speaking, without end — he could give every New Yorker $1,000 tomorrow and retain his place (after David Koch) as the second-richest guy in town.

The practice's sordid edge did, occasionally, slip into view. It was perhaps at its rawest in 2004, when the liberal goodwill the new mayor had gotten simply from not being Rudy Giuliani — who had once tried to shutter the Brooklyn Museum for sacrilege — wore off. That was the beginning of the mayor's first reelection campaign, and he developed a particular and personal dislike for one challenger, the young City Council Speaker Gifford Miller. My colleague Lizzy Ratner and I heard that a deputy mayor was bluntly threatening cultural institutions that giving Miller money would be seen as "disloyal," and reported that the official "wasn't talking about recent government support from City Hall. She was referring to about 10 years and tens of millions of dollars worth of arts patronage from Mr. Bloomberg himself."

The next year, Bloomberg gave $20 million to 400 different groups — many of whose staffers would, at the next election, show up to testify in favor of extending the city's two-term limit, as Sol Stern and Fred Siegel wrote in 2011, describing what they saw as "the most discomfiting aspect of the Bloomberg mayoralty: the mayor's use of his own personal resources to buy himself not only political power but also political peace."

Bloomberg's money flew in all directions, and rarely with any explicit suggestion of debt. City Hall reporters work in a press room he paid, personally, to refurbish, and for years were entertained on his dime at annual Gracie Mansion dinners. (After raised eyebrows, they started paying for them.) But Bloomberg frankly bought off potential political threats. The various county Republican Parties, whose rank and file (such as they are) rankled at elements of Bloomberg's muscular assertion of government power to ban smoking, trans fats, and giant sodas, were wholly owned subsidiaries of the mayor, who gave larger contributions than they'd ever seen or were likely to see again. Then there's Al Sharpton, who picked up one six-figure donation from a Bloomberg-backed charity at a crucial moment and whose donors at the National Action Network aren't disclosed.

The most obstreperous advocates, the ones who remained noisy as their Giuliani-era allies fell quietly away, are among the few who will speak openly of the change. One is Patrick Markee, the veteran Senior Policy Analyst of the Coalition for the Homeless who recalled a 2010 battle over City Hall's plan to charge homeless families rent for shelter space.

"Lots of not-for-profit groups that work in the field were quiet and sat on the sidelines while this was happening, and didn't speak up publicly, and then public records kind of indicated that a lot of those groups that received large personal donations from the mayor," Markee said. "I think you would have seen a lot more vocal opposition to Bloomberg's policies if it hadn't been for his using his vast wealth in a very tactical way."

One of Giuliani's leading antagonists had been Norman Siegel, who led the New York Civil Liberties Union in the 1990s, and who saw a muted response even as complaints over the New York Police Department's treatment of protesters, monitoring of Muslim immigrants, and stop-and-frisk policing mounted.

"In the Giuliani years I would talk to people who work for not-for-profits and they would be willing to participate" in civil liberties lawsuits, he said. "During the Bloomberg years, it was much more difficult because some groups would say 'Well, you know we're getting funding from Bloomberg, we like Bloomberg,' or toward the end people were more unprepared to take him on because they had this delusional thought that somehow when he's in his foundation world, if they're nice to him, they'll get rewards and get grants from his foundation."

This is a big city, and Bloomberg's money was hardly the only factor in the civic peace he imposed — or the only reason it's about to erupt into a much noisier place.

Howard Wolfson, a top adviser for the last four years, called the suggestion that Bloomberg's money had silenced potential critics "overblown and inaccurate," and noted that he regularly walked past protesters into City Hall.

"If New York City has been less noisy, it's because it's better run," he said.

And a former aide, Stu Loeser, described what is certainly another reason for the calm of the Bloomberg years.

"This presumes that Mike cared about being criticized and wanted to limit criticism," he said of the suggestion that the mayor would pay for silence. "To a real degree, the opposite was true. He felt if special interests weren't attacking him, he wasn't doing enough. He relished the attacks on congestion pricing and trans fats and school standards and the smoking ban and so many other policies because he thought he was right on the issues, if not the politics. And he didn't care much about the politics."

Indeed, lobbyists in the Bloomberg era regularly advise their clients to avoid confrontation. You would not, for instance, want to be told — as one vocal foe reportedly was — "'Come January 1st, when I am out of office, I am going to destroy your fucking industry.'"

Indeed, it's not just the money. The coming de Blasio wars are probably overdetermined: The new mayor has a genuine belief in the value of consultation in its own right, and if you consult New York, you're likely to get a noisy response. The question for de Blasio isn't whether he will face louder demands, or even whether he'll be able to manage them: It's whether, in this new city, he'll be able to hold the line after he's made his consultative decision.

But organized civil New York, after a decade of unprecedented quiet, is going to have to get used again to fighting for public money, with no mayoral slush fund to bail them out or reward compliance.

"The nonprofits and the cultural institutions have been worried about this day for years, and there's no way to prepare yourself," said Siegel, the Bloomberg critic and Giuliani biographer. "They're going to have to stand and fight, stand in line and fight with every other interest."

This is just a return to municipal reality of course, but it may be one that residents of the luxury city of New York aren't quite prepared for. Indeed, civic peace and quiet has been one of the luxuries of the Bloomberg era.

Muzzio compared the new reality to "an addict in withdrawal."

"The money ain't going to be there and you're going to see shrinkage and more conflict," he said. "It's going to be the old days."