Former three-term U.S. Sen. Al D’Amato and chief deputy Nassau County executive Rob Walker dealt a dramatic one-two punch to their self-described “friend” Sen. Dean Skelos at his federal corruption trial Friday with damaging testimony about his efforts to use his influence to help his son, Adam Skelos.

D’Amato, who was probed for ethical missteps but never charged during his terms in office, said in surprise testimony that after a meeting set up by the senator, Adam tried to get D’Amato’s Park Strategies lobbying firm to hire him, but the firm was “adamant” that it couldn’t hire the son and lobby his father as Senate majority leader.

“Under no circumstances could we bring him into the firm,” said D’Amato, 78, who packed the Manhattan federal courtroom with the rare testimony from one GOP power broker against another. “The appearance of impropriety was such that we could not work together.”

StoryEx-official: Skelos aide set up meeting with stateSee alsoRead the complaint vs. SkelosMore coverageSenate Majority Leader Dean Skelos, Adam Skelos face corruption charges

Walker, following D’Amato, gave the first public acknowledgment that he is under scrutiny in a separate federal corruption probe on Long Island, while telling jurors how Sen. Skelos pressed County Executive Edward Mangano at a January police funeral to fund a contract with AbTech Industries, a firm that had hired Adam.

“He was just asking about a payment, were they getting paid anytime soon,” testified Walker, who was walking behind and immediately made a call, reporting back to the two that the money would arrive soon. “The senator said thank you and that was the end of the conversation,” Walker recalled.

Mangano will not testify at the trial, Skelos’ lawyer said at a sidebar conference with the judge, according to a transcript, because the county executive has exercised his 5th Amendment right and prosecutors refused to immunize him.

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Newsday has previously reported that Walker and Mangano are under scrutiny in a federal political corruption probe on Long Island centered on restaurateur Harendra Singh. Walker didn’t name Singh, but said he was testifying with testimonial immunity to protect him in another investigation.

He said the judicial immunity order protected him only against use of his Skelos testimony in the Long Island probe, but did not protect him against any possible charges. He said that probe involves county contracts for campaign donors, and steering business to someone with personal ties.

Afterward his lawyer, Brian Griffin, told reporters Walker would survive his encounters with both the Skelos and Singh probes unscathed. “He has done nothing wrong, he has nothing to hide,” Griffin said.

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Dean Skelos, 67, and Adam, 33, are charged with using Dean’s clout to get Adam work from developer Glenwood Management, malpractice firm Physicians Reciprocal Insurers, and AbTech, and then helping AbTech by pressuring Nassau to fund a $12 million stormwater-pollution contract and pushing legislation in Albany.

Walker’s testimony about the conversation with Mangano at an NYPD funeral in Brooklyn filled a key gap for prosecutors. That is one of the corrupt episodes of official action to help AbTech and Adam alleged by prosecutors in the Skelos indictment.

A “friend” and ex-Assembly colleague of Skelos, Walker first learned of AbTech’s hope to supply stormwater pollution equipment to Nassau in an email from Adam, and he said Mangano — after getting a “contact from the senator” — called later to ask about progress on a contract.

Walker said the project — which ultimately only got $150,000 in funding — got his full attention. “Because of the senator,” Walker explained. “To make sure he’s in a good frame of mind about the county.”

Walker said Skelos was also involved in meetings in Albany about trying to push Nassau legislation for public-private partnerships that would increase state aid to fund “stormwater” projects of the sort AbTech planned.

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Eventually, he testified, he was distanced from the process because despite his friendship with Skelos he was suspected of trying to slow down the AbTech deal. “It came back that the senator didn’t want me in some of the meetings,”

Walker also insisted that he wasn’t giving testimony against Skelos in hopes of lenient treatment from the government in the Long Island probe. “I have no idea where it sits but I am ready to answer any questions they may have,” he said.

D’Amato, 78, of Lido Beach, a politician known as “Sen. Pothole” who was never viewed as an ethical angel himself during his time in office, described himself as a Senate constituent of Skelos and longtime admirer, and tried to downplay the impact of his testimony as he left court.

“I didn’t testify against my friend,” he told reporters. “I just answered the questions.”

Before describing Adam’s bid for the lobbying job, D’Amato testified about efforts he made in April 2013 to intervene with Dean on behalf of Physicians Reciprocal, the Roslyn malpractice firm that hired Adam at his father’s request, only to have him refuse to come to work and allegedly threaten a supervisor.

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D’Amato said Park Strategies lobbied for the malpractice firm, and a partner asked him to help. He made an appointment and was driven from his Uniondale office to Skelos’ Rockville Centre headquarters, in hopes a personal plea could get Dean to tell his son to fly right.

Instead, he testified, Skelos made no such offer. He said “Adam needed the job. His wife was expecting,” D’Amato testified.

What did Dean offer to tell Adam? prosecutor Rahul Mukhi asked. “He didn’t,” D’Amato answered.

What was Dean’s tone during the conversation? the prosecutor asked. “It would be difficult to characterize,” said D’Amato, giving little indication that he relished the opportunity to testify against his fellow Republican.

At some later unspecified date, D’Amato said, Dean asked him to meet with Adam to “give him some advice.” D’Amato said he and his brother Armand spoke to Adam about some of the work and clients he had, and advised him that he might “be required to register as a lobbyist.”

Six to eight weeks later, D’Amato said, the initial meeting turned into a pitch from Adam to work for or with Park Strategies during a lunch in Manhattan with D’Amato and his son Christopher. The feeler was “forcefully” rebuffed as an “absolute impossibility,” he testified.

“I thought the appearance would be one that raises questions about conflicts,” D’Amato said.

Met by a battalion of cameras as he left the courthouse, D’Amato was asked if he felt bad for the Skeloses. “I think you have to have a certain feeling, yes,” he answered.

U.S. District Judge Kimba Wood, whom D’Amato praised for her beauty when he recommended her for the bench in 1988, said the trial would resume Tuesday, when the prosecution is expected to rest.