SACRAMENTO, Calif. — Even for a political town where claims of wrongdoing are woven into the competitive fabric, Sacramento has seen an unusual burst of activity alleging ethical breaches by the powerful.

On a single day this past week, the Democratic leader of the state Senate stood before the Capitol to address the latest allegations in an FBI corruption probe, a Republican state senator took the witness stand to testify he had not engaged in money laundering, the state’s political watchdog handed down fines to one current and two past lawmakers who admitted campaign finance violations, and three former government officials who were recently fined for not registering as lobbyists sat through a required ethics class.

The instructor went over rules that forbid lobbyists from giving officials gifts worth more than $10 a month, explained exceptions — such as those that allow lobbyists to entertain officials at their homes or invite them to a wedding — and advised the 74 lobbyists in the audience not to deliver campaign checks to politicians’ offices.

“This is the part where I used to talk about what was known as ‘shrimp scam’ in the late ’80s and early ’90s, which was an FBI sting,” said instructor Cary Rudman, chief counsel to the Senate Committee on Legislative Ethics.

He explained that the case involved undercover agents posing as the operators of a shrimping business, who offered bribes in exchange for beneficial legislation. The case eventually led to the convictions of several lawmakers, staff members and lobbyists, Rudman said.

The history lesson may no longer be necessary.

“As most of you know, there has been some recent activity,” Rudman told the class. “Allegations of corruption are here.”

The high-profile FBI investigation of California state Sen. Ron Calderon has roiled the Capitol since agents raided his offices in June. The case has taken dramatic turns in recent weeks as Al Jazeera America published a 124-page affidavit in which the FBI alleges Calderon accepted $88,000 in bribes from an undercover agent and a Long Beach hospital executive.

Calderon, a Democrat, responded this week with a federal court filing alleging the government intentionally leaked the affidavit, and that two other Democratic senators — Darrell Steinberg of Sacramento and Kevin de Leon of Los Angeles — were in fact the focus of the FBI’s probe.

No charges have been filed. Steinberg and De Leon have each said prosecutors told them they are not the subject of the federal investigation. Calderon’s attorney has said his client has not done anything illegal.

On Thursday, the commission fined former Democratic state Sen. Dean Florez, $60,000 for misusing campaign funds; fined former Assemblyman Mike Roos, a Democrat, $3,000 for breaking state law by making political contributions while he was a registered lobbyist; and finalized a settlement with current Assemblyman Luis Alejo, a Democrat, in which he was required to return $21,000 to an independent group that had illegally coordinated with his campaign.