Mayoral challenger Garry McCarthy returned to City Hall Wednesday — for the first time since Mayor Rahm Emanuel fired him — to hammer his former boss on the issue of ethics and corruption.

Emanuel has pushed through a seemingly endless string of ethics reforms in an effort to turn the page from the Hired Truck, city hiring and minority contracting scandals that cast a giant shadow over former Mayor Richard M. Daley’s 22-year reign.

But McCarthy said the mayor who fired him is not fooling anybody. He argued the “scandals that have enveloped” the Emanuel administration “encompass the breadth” of city operations.

They range from the contract kickback scheme and ethics scandal that claimed two Chicago Public Schools CEOs to the sexual abuse and school cleanliness scandals at CPS.

He mentioned: the $2 million bribery scandal that has tainted Chicago’s red-light camera program; racism in the Department of Water Management; the “repeated sanctioning” of the city’s Law Department for withholding documents from defendants in civil cases and the mayor’s decision to withhold the Laquan McDonald shooting video until after the 2015 election.

McCarthy further argued that the mayor’s personal emails — released to the public only after yet another court fight — reveal the “depth of Emanuel’s pay-to-play philosophy.”

“Everybody knows right now that, if you want a city contract, you make a campaign donation to Rahm Emanuel and you get that contract,” McCarthy said, promising a “zero tolerance policy.”

“Read the mayor’s emails. You all got them. And the pay-for-play that’s being reported … over and over and over. It’s really obvious what happens.”

McCarthy said it’s high time the mayor stop trying to divert public attention from major scandals. It’s not working.

“How `bout not responding to the knowledge of the CPS sex scandal for days, hoping that it would pass? Maybe if I do another press conference, maybe nobody will notice. Make an announcement. Let’s get a tunnel going to O’Hare. How `bout that?” McCarthy said.

McCarthy even went so far as to liken Emanuel’s decision to close mental health clinics and a record 50 public schools to the now-raging political controversy over the separation of children from their parents at the U.S. border.

“We need a compassionate government. I don’t think we have that right now,” McCarthy said.

Emanuel’s communications director Adam Collins argued that the mayor’s “actions to change the culture at City Hall couldn’t be more clear” and put the lie to McCarthy’s broadside.

“The very first thing the Mayor did when he took office was to overhaul the city’s ethics rules and shut the revolving door between working for city government and lobbying city government,” Collins wrote in an email.

“In the seven years since, he reformed city procurement and made it more transparent, gave new protections to whistle-blowers, expanded the Inspector General’s role and authority, reformed hiring practices to end the decades-old Shakman decree and so much more.”

McCarthy lost his job as Chicago’s $260,044-a-year police superintendent in the furor that followed the court-ordered release of dashcam video that showed white Chicago Police Officer Jason Van Dyke firing 16 shots at black teenager Laquan McDonald.

After claiming he had McCarthy’s back for weeks, Emanuel fired him on Dec. 1, 2015, saying McCarthy had become a “distraction.”

On Wednesday, McCarthy once again pointed to former Corporation Counsel Steve Patton as the architect of that “cover-up” and behind the decision to withhold the video until after the 2015 mayoral election.

He argued once again that Patton lied to the City Council to win approval of a $5 million settlement to the McDonald family before a lawsuit had even been filed by saying now-indicted Chicago Police Officer Jason Van Dyke acted within the scope of his authority — only 18 months later did Patton tell the Chicago Sun-Times that Van Dyke had murdered McDonald.

“There’s a crime called official misconduct,” McCarthy said Wednesday. “I believe there’s a criminal case to made.”

Patton countered, “There’s no misconduct here. I called it straight with the City Council like I always tried to do. I told them what the facts were.”

The former corporation counsel said the transcript of his testimony before the Finance Committee shows “the exact opposite” of what Garry is now claiming.

“The fact that we were likely to lose the case because a jury would find the shooting was not justified was the entire reason the Law Department recommended that the city settle the case for $5 million,” Patton said Wednesday.

“As to McCarthy’s suggestion that the settlement … was somehow part of a cover-up, he’s on record as saying the exact opposite on numerous occasions before he decided to run for mayor.”

The mayor has emphatically denied keeping the McDonald shooting video under wraps to get past the election. But he has acknowledged he “added to the suspicion and distrust” of everyday Chicagoans by blindly following the city’s long-standing practice of withholding shooting videos to avoid compromising criminal investigations.

The McDonald case — and the role that Emanuel and McCarthy played in it — is certain to dominate the campaign and make it difficult for both men to win black votes.