ALBANY—Earlier this month, Michael Bloomberg and Eliot Spitzer emerged from the Governor’s midtown office with great fanfare and announced that they were ready, in principle, to support City Hall’s sweeping plan to reduce traffic and air pollution in New York, which includes a proposal to charge cars for entering midtown Manhattan.

Not that it mattered.

The real show, for those interested in divining the fate of the Mayor’s sweeping urban-sustainability PlaNYC, took place in Albany this week, where a stoop-shouldered, graying cipher of a man shuffled down the hallway in the state Capitol behind the Assembly Chamber, and slowly mumbled to a handful of reporters in a gravely voice, “We’re going to conference it,” and “We’re going to talk about it.”

Thus spoke Sheldon Silver, the 63-year-old Democratic State Assembly Speaker who led his party during the dark years under Republican Governor George Pataki and who has stubbornly refused to fade away now that, technically, there’s another Democrat in Albany that outranks him.

It has often seemed in the past few years that it is Mr. Silver who has the final say on anything significant that happens in New York—City or State. Answerable for his position only to a few thousand voters in his Lower East Side legislative district and the 108 Democratic Assembly members, Mr. Silver is defiantly impervious to all other public and political pressures.

Two years ago, after months of intense pleading from the Mayor, construction labor unions and the New York Jets, Mr. Silver inserted a shiv into the faintly beating heart of Mr. Bloomberg’s plan to attract the Olympics to New York City by vetoing a proposal to build a stadium on Manhattan’s West Side.

More recently, it was Mr. Spitzer who was on the receiving end of one of Mr. Silver’s clinical displays of willful inertia. Elected by a landslide after running on the naïvely energetic slogan “Day One, Everything Changes,” the Governor found his plans for capping education costs, closing hospitals and fighting the health-care unions over health-care spending mired in a swamp of studied indifference from Mr. Silver.

And now, with all eyes on Mr. Silver as he and his members mull the fate of another major city initiative, things have once again reverted to form.

“That’s the way Albany has worked—everything has to go through the Assembly Speaker,” said former Governor Mario Cuomo, who was in his third term in Albany when Mr. Silver became the Speaker.

“People thought he would be eclipsed when there was a Democratic Governor,” added former New York City Parks Commissioner Henry Stern. “But he’s more assertive than ever.”

The ability of the State Legislature to exercise influence over New York City in particular is the result of years and years of checks placed on the city’s perceived profligacy and corruption by an antagonistic state government.

“Part of it goes back to the desire for upstate to retain government accountability in the city. Back a century ago, the city was perceived as the center of corruption,” said Robert Ward, director of research at the Public Policy Institute of New York. “Anything other than property taxes, like income taxes, sales taxes, they have to be approved from the state.”

It’s also a remnant of the city’s fiscal crisis of 1975, when the city was bailed out by the state, but was forced to surrender discretion over many aspects of its finances, as well as the City University system, the transportation system and a good portion of its public workforce.

“The city lost 60,000 cops, teachers, clerks, union workers, its university, contracting for its bridges and tunnels—it gave up a boatload,” explained Bill Cunningham, a former advisor to Mr. Bloomberg and former aide to then-Governor Hugh Carey who is now managing director at Dan Klores Communications.

To pay off billions of dollars’ worth of bonds the state took out to keep the city afloat, the city agreed to give the state the first $500 million it earned from the city’s sales tax. Whatever the city raised after that, it could keep.

And in a move whose consequences are still being felt, the state gained the ability to reign in the city financially through a Financial Control Board.

But while Albany as a whole has the constitutional ability to impose its will on the city, it is Mr. Silver who has emerged as a singular kingmaker there.

His Republican counterpart in the State Senate, Majority Leader Joe Bruno—one of the “three men in a room” who run the state—is clinging to a shrinking majority and is heavily indebted to the Mayor, who has contributed generously to the campaign coffers of his members. He is in a position that requires that he pick his fights, to say the least.

And the initially aggressive posture toward the Assembly of Mr. Spitzer, who rode into office on a wave of theoretical voter discontent with Albany, has only served to rally the Democratic majority around Mr. Silver for the foreseeable future.

It’s not by accident, according to Alan Chartock, a professor at the University at Albany, and executive publisher of a newspaper focusing exclusively on state government, The Legislative Gazette.

“It’s interesting, what it comes down to for regular Assembly Democrats …. They almost always are with their own leader,” said Mr. Chartock. “It’s like playing for team—and team spirit.”

“Shelly is the person to go to if you want business in the Assembly,” Mr. Stern said. “Who else would you go to? He has no rivals in the Assembly.”

The answer to the question of whether things must ever be so is: probably.

There were efforts in the past to change the state’s Constitution, but they failed twice. Once in 1977, when Mr. Cuomo was the Secretary of State. Then again in 1997, just after he left office. Both times, Mr. Cuomo said, he supported the effort that would have let voters change the Constitution and, among other things, possibly shift more decision-making power away from Albany and back to City Hall.

“The Democrats were not for it,” he said. “The Republicans were not really for it. Because a Constitutional change threatens the incumbents, they persuaded the people not to vote for it.”

The result is what we see today.

Mr. Bloomberg introduces his plan, which, as part of a wider transportation initiative to promote mass transit and decrease car traffic, would charge motorists $8 a day to drive on Manhattan streets below 86th Street during business hours.

He is backed by a meticulously assembled coalition of labor, business and environmental leaders. The plan receives mostly positive reviews from the press. The Governor gives the Mayor conditional backing, as does the State Senate Majority Leader and City Council Speaker Christine Quinn.

And as of press time, as the legislators in Albany prepared to disperse for the summer, all of them, once again, were waiting for Mr. Silver.

“The enigma thing—whatever the degree of truth in it—it certainly enhances Silver’s ability to negotiate, because it keeps everyone else guessing,” said Mr. Cunningham, somewhat admiringly. “And in every negotiation, up to a certain point, that’s a good thing.”