ST. PAUL — Michael Brodkorb once was the bane of Minnesota Democrats, a savvy and aggressive operative whose scorched-earth approach to politics — showcased on a blog called “Minnesota Democrats Exposed!” — fueled his rise to dual roles as deputy chairman of the state GOP and chief spokesman for Senate Republicans.

Today, he’s as toxic to his own party as he ever was to Democrats. Fired late last year from his Senate job after an adulterous affair with the majority leader — his boss — Brodkorb is now threatening a $1.5 million wrongful termination lawsuit that his attorney says could expose more than a dozen other Capitol affairs.

“I call that extortion or blackmail and I will continue to do so,” Cal Ludeman, the Senate’s chief administrative employee, said this week. Brodkorb’s lawyers called the comment defamatory.

Whatever the motive, the mere possibility Brodkorb may expose alleged infidelities has rocked Senate Republicans and sent politicians of every stripe running for cover.

At a regular end-of-week briefing for Capitol reporters, the Senate’s No. 2 Republican, Sen. Julianne Ortman, said a variation of “no comment” eight times in less than five minutes when questioned about Brodkorb. Numerous Republican senators approached by The Associated Press said they would not discuss him.

Ludeman fired Brodkorb without public explanation in late December, one day after Sen. Amy Koch abruptly quit her leadership post. When Koch later admitted she’d had an affair, widespread speculation had Brodkorb as the other half. But that wasn’t confirmed until this week when Brodkorb’s attorney said the two, both married to other people, had been in an intimate relationship.

Brodkorb’s potential lawsuit rests on a gender discrimination claim that even his attorney called “new and creative:” that he was treated differently as a man who had an affair with a female superior, in contrast to numerous female legislative employees he claims never lost their jobs despite affairs with male legislators.

“He intends to depose all of the female legislative staff employees who participated in intimate relationships, as well as the legislators who were party to those intimate relationships, in support of his claims of gender discrimination,” according to a legal document Brodkorb’s lawyers filed this week with the state. Brodkorb’s attorney, Philip Villaume, told The Associated Press on Friday that Brodkorb has evidence of “10 to 15” such affairs. He wouldn’t describe the evidence.

Brodkorb hasn’t spoken publicly since he was fired and declined to comment for this story. Koch also has repeatedly refused comment.

Villaume said he can understand why legislators might be nervous. “Human nature being what it is, I guess I’d be a little uneasy about it.” But, he added: “It’s not our purpose to unnerve people, to upset their lives. Our job is to protect the legal interests of Mr. Brodkorb.”

Brodkorb, 38, began working on Republican campaigns in the 1990s and became an expert in “opposition research” — digging up incriminating information about political opponents. As founder and operator of “Minnesota Democrats Exposed,” Brodkorb from 2004 to 2008 maintained a stream of posts questioning the character and integrity of dozens of prominent Democrats.

Many were gleeful when he was fired, and some were happier still to see him threatening litigation that could hurt his own party. Brodkorb’s notice of claim warns of possible separate legal actions against a slew of Republican leaders who had a hand in his firing.

“Feel like I need a cigarette after that,” Javier Morillo, president of the state chapter of the Democratic-allied Service Employees International Union, tweeted shortly after Brodkorb’s lawyers finished a news conference where they talked about investigating affairs.

But Democrats at the Capitol were far more restrained. Brodkorb’s legal filing suggested he could implicate some in their party, too.

“I think we all have to be very careful about what gets said relative to the Brodkorb issue,” said the Senate’s Democratic leader, Tom Bakk. Still, he noted taxpayers likely would be on the hook for any settlement — Brodkorb is seeking at least $500,000 — and said the allegations “bring a great deal of dishonor to our institution.”

Asked who was responsible for that dishonor, Bakk responded: “It’s certainly not the Democrats.”

Sen. John Marty, a Democrat and 25-year Capitol veteran known as a guardian of legislative ethics, admitted that “you hear stories pop up now and then” about infidelities committed in the heat of the state’s yearly, months-long legislative sessions. But he said he felt Brodkorb was “clearly trying to get some money out of the Senate.”

“It’s just an ugly situation,” Marty said. “I’m trying to stay as far away from it as I can.”