Though it hit the state Capitol like a tidal wave Thursday, the arrest of Assembly Speaker Sheldon Silver on federal corruption charges isn’t the first time a legislative leader has been charged with wrongdoing.

But it could turn out to be a watershed.

Former Assembly Speaker Mel Miller, also a Democrat, was forced out of office in 1991 following his conviction on charges that he had cheated his private legal clients. Miller served out a session as speaker as he awaited trial, but he lost his office after his conviction. He was later cleared on appeal, but decided not to return to politics.

As in Miller’s case, Assembly Democrats said they would stand by Silver based on both his long service to the chamber and the presumption of innocence.

That presumption was ultimately borne out at the end of Joseph L. Bruno’s long legal road. The former Senate Republican majority leader was charged in 2009 with taking bribes disguised as consulting fees. He was convicted, only to have the verdict reversed by the U.S. Supreme Court. He was ultimately acquitted in a second trial last year.

The accusations against Silver are similar in nature, since they too focus on bribery in exchange for political favors. But the case against the Manhattan Democrat is notable for its clarity and the way it casts light on the secretive workings of the Legislature and the even more secretive outside income earned by many of its members.

“The charges against Mel Miller were obscure, dense pieces of law,” recalled Bob Bellafiore, who covered Miller’s downfall as a Capitol reporter before working in the Pataki administration.

“Any 5-year-old can understand the case against Speaker Silver,” said Bellafiore, now a public affairs consultant. “It’s a very simple case of ‘You scratch my back and I’ll scratch yours.'”

U.S. Attorney Preet Bharara of New York’s Southern District alleges that Silver extorted bribes and kickbacks disguised as legal fees from real estate interests in exchange for legislative favors and doled out public dollars and other benefits to a leading New York City physician in exchange for client referrals.

Due to the size and scope of Silver’s alleged schemes, which brought in $4 million that he deposited in numerous bank accounts, comparisons with other cases are difficult to make.

“It was a whole different set of circumstances,” said Miller, now a lobbyist with Park Strategies.

Most significantly, Miller was never charged with misconduct related to his office. The complaint facing Silver, in contrast, charges him with engineering the machinery of government for his personal benefit.

E.J. McMahon, another Pataki veteran who now runs the Empire Center, agreed: “The Mel Miller case was about Mel Miller. It wasn’t about the whole institution looking over its shoulder.”

If the charges against Silver are far worse than those faced by any Capitol leader in recent memory, the media landscape where it will be covered has evolved as well.

“In 1991, there wasn’t a blog; there weren’t websites; there wasn’t a 24/7 news cycle,” said Steve Greenberg, who was Miller’s press secretary and now runs a public relations business.

Miller isn’t the only speaker before Silver to have encountered legal difficulties in recent decades. Stanley Steingut, who led the chamber from 1975 through 1978, was indicted for allegedly trying to secure political donations for his son’s New York City Council campaign. The charges were ultimately dismissed.

Since Miller left office, the list of the Capitol’s elected miscreants has only grown larger and more notorious.

Between 2000 and this year, at least 30 lawmakers — in both parties, from the Assembly and Senate — have faced charges, often leading to conviction or departure from office.

The misdeeds run the gamut: Vito Lopez, Dennis Gabryszak and Micah Kellner left the Assembly after facing sexual harassment allegations; Sens. John Sampson and Shirley Huntley were charged with embezzlement; bribery was the case against Assemblymen Eric Stevenson and William Boyland and Sens. Carl Kruger, Vincent Leibell and Malcolm Smith, among others. Also, Senate Republican Deputy Majority Leader Tom Libous faces a federal charge of making false statements to the FBI.

Sen. Pedro Espada fell to tax evasion after leaving office, and William Scarborough currently faces federal and state charges relating to abusing the per diem system and campaign finance laws.

The length of that list — by no means comprehensive — explains why Silver’s legal saga will once again raise questions about the rules governing the outside income earned by the members of what’s ostensibly a part-time Legislature.

When Gov. Andrew Cuomo’s short-lived Moreland Commission on public corruption tried to probe outside incomes, lawmakers fought back — with Silver in the forefront, spending public funds to fight the investigation in court. Cuomo then shut down the Moreland Commission in April after securing a modest package of ethics reforms. But Bharara picked up the investigation, and merged its partial finding what a pre-existing probe of Silver’s work.

The debate over outside income issue was back in the news just days before Silver’s arrest.

Cuomo, in his State of the State address, suggested giving lawmakers a raise — something that hasn’t happened since 1999 — but linking it to limits on their private earnings.

Dozens of lawmakers have their own law practices or consultancies, or other businesses that may or may not intersect with their legislative duties. Public disclosure is minimal, enforcement is viewed as lackluster and the penalties for violation are notoriously light.

Bharara has warned that more cases are imminent, and lawmakers have been put on notice.

“There are others with substantial outside income,” noted Blair Horner, legislative director at the state Public Interest Research Group.

Cuomo, in what turned out to be a prescient remark, said people are wary of lawmakers who earn huge sums from outside jobs.

“What hits the suspicion button for New Yorkers is you’re a legislator (and) you make $400,000 in a business,” Cuomo said before his speech — and before Silver’s arrest.

“Is the outside income,” he asked, “in any way connected to your position as a legislator?”