Since he was first sworn in as mayor nearly eight years ago, Bill de Blasio has been dogged by allegations of corruption and ethical breaches.

Claims have ranged from the familial — He used his NYPD security detail to shuttle his son back-and-forth to college and move his daughter out of her apartment — to the political, as when he faced accusations of doling out business favors to real estate developers who contributed hundreds of thousands of dollars to his campaign and causes.

But through it all, de Blasio has never been charged with or otherwise formally accused of a crime — infuriating political watchdogs.

“It is really shocking to see how much de Blasio has been able to get away with, and it bodes very poorly for New York City,” said John Kaehny, executive director and founder of Reinvent Albany, a good government group active in the city. “You’re reminded that there are still so many things that are dysfunctional and corrupt in New York.”

Despite the various investigations into de Blasio’s conduct, a former top aide to the mayor said he never seemed especially worried about any of it and privately displayed a “lack of humility” about the gravity of the accusations against him.

“None of this s--t ever seemed to faze him,” the ex-aide, who requested anonymity, told the Daily News. “He was very flippant about it. He always put it in a bucket of: New Yorkers don’t really care about this sort of thing.”

An especially brazen example of de Blasio’s transgressions came to light just a few weeks ago.

After de Blasio managed to block their release for over two years via legal means, a Manhattan court on Dec. 9 ordered the unsealing of two confidential letters that the Conflicts of Interest Board sent to the mayor in 2014 and 2018 revealing he violated city ethics law several times by soliciting political donations from companies with business before his administration.

The letters noted that de Blasio’s law-defying solicitations came in spite of the fact that the board warned him three times his actions were violating conflict of interest laws meant to safeguard against “coercion and improper access” to City Hall.

A former senior city official who served during de Blasio’s tenure said the mayor’s flagrant nose-thumbing at COIB is beyond the pale.

“To be told once by the Conflicts of Interest Board that you’re out of compliance with the city rules is bad, but to continue doing it after you’ve been warned by the Conflicts of Interest Board is almost a Trumpian display of disregard for the rule of law,” the former city employee said.

The ex-official also bristled at the fact that it took a two-year court battle for the damning COIB records to be released — especially given de Blasio’s 2013 campaign promise that he’d be transparent with the public.

“This was not a very transparent administration,” said the former official, who requested anonymity. “Look at the number of lawsuits that had to be filed to get basic documents that a transparent administration would have made public.”

Another ethical controversy that recently ensnared de Blasio involved questionable usage of his taxpayer-funded NYPD security detail.

In a blistering report released in October, the city Department of Investigation found de Blasio and his family misused the detail for a variety of personal and political reasons, such as picking up relatives at the airport and serving as a “concierge service” for Dante de Blasio, the mayor’s son, including driving him to and from college in Connecticut.

The report also concluded de Blasio dished out nearly $320,000 in public funds to have his security team travel with him and campaign staffers across the country during his failed 2020 presidential bid.

And even though COIB ruled that he must reimburse taxpayers for the campaign expense, de Blasio has refused to do so, claiming he had the right to bring along his NYPD detail on the trail and saying he is still appealing the board’s decision.

“The guidance I have received is from the NYPD,” he said in October about his usage of the detail.

Yet, the Department of Investigation referred Howard Redmond, the NYPD inspector in charge of de Blasio’s security, to the Manhattan district attorney for potential criminal prosecution over allegations that he sought to cover up the scandal by destroying phones and other evidence. It remains unclear if the DA will act on that referral.

Arguably the most serious scandal de Blasio has faced in office played out during his first term when federal prosecutors in Manhattan were investigating him over allegations that he was using a nonprofit as a political pay-to-play slush fund, to which deep-pocketed donors could contribute in exchange for favors from City Hall.

According to reports from the time, the probe focused on donations politically connected businessmen and others made to de Blasio’s Campaign for One New York, which he used as a fundraising vehicle for various policy pushes, in exchange for favors from the administration, like building permits and city contracts. Some of the donations scrutinized as part of the federal inquiry were the same that prompted COIB to reprimand de Blasio in 2014 and 2018.

“It’s been one scandal after another — the Campaign for One New York, which we’re still learning new facts about, Rivington ... his campaign for president, his use of his police detail as personal movers and Uber drivers,” said outgoing Democratic Manhattan Councilman Ben Kallos, a longtime de Blasio critic.

“Rivington” is a reference to Rivington House, a Lower East Side building that an indebted nursing home operator — and major de Blasio campaign contributor — sold for profit to a luxury condo developer after the mayor’s administration abruptly lifted a property deed restriction in 2015.

In a wonky legislative push, Kallos tried, and failed, to pass a bill this month that would have required de Blasio to disclose how he plans to repay hundreds of thousands of dollars he still owes to a law firm that represented him during probes into the Rivington and CONY scandals.

Kallos added, “I’m sure there’s more that we still haven’t learned about.”

The CONY investigation produced indictments against several top de Blasio donors, including businessmen Jona Rechnitz and Jeremy Reichberg, as well as three senior NYPD cops and ex-Correction Department union boss Norman Seabrook, among others.

But de Blasio was able to dodge criminal liability, though the Manhattan U.S. attorney’s office hinted in a 2017 statement that the outcome could have been different if it were not for “a recent change in the law,” a reference to a Supreme Court decision that overturned a high-profile public corruption case at the time.

A former Manhattan federal prosecutor, who was not involved in the de Blasio probe but served in the U.S. attorney’s office while it was active, suggested the Supreme Court ruling may have been the mayor’s saving grace.

“Let’s just say you have enough evidence under the previous standard, but not under the new standard — then you’re in a very complicated spot as a prosecutor,” the ex-fed said, speaking only on condition of anonymity.

Though de Blasio was never charged with any crimes while in office, Kaehny, the Reinvent Albany rep, said he hopes the mayor’s checkered past is revisited if he opts to run for governor next year.

“He should pay a political price,” Kaehny said. “It should be brought up if he runs.”