If anyone would know Hillary consigliere Cheryl Mills’ reputation for obstructing investigations, it’s FBI Director James Comey. He complained about her lack of cooperation while probing Clinton scandals in the 1990s. Yet he agreed to give Mills immunity from prosecution in his probe of Hillary’s illegal e-mails as secretary of state, where Mills was chief of staff.

As a Whitewater investigator for the Senate in the mid-1990s, Comey sought information from Mills; but wouldn’t you know, the then-deputy White House counsel claimed a burglar stole her notes.

Comey concluded that Hillary Clinton ordered Mills to block investigators. The obstruction, the Senate committee found, included the “destruction of documents” and other “highly improper . . . misconduct.”

Two years later, Mills was in the middle of another Hillary scandal, involving the then-first lady’s integration of White House and Democratic National Committee computer databases.

This time the House subpoenaed information from Mills, who not only withheld the documents but, a government committee said, “lied under oath” — prompting staff lawyers to send a criminal referral to the Justice Department demanding prosecutors charge Mills with obstruction of justice and perjury.

In 2000, a Commerce Department official testified that Mills ordered her to “withhold” from investigators e-mails and other documents exposing yet another scandal involving the first lady — the selling of seats on foreign trade junkets for campaign cash.

At the same time, a federal judge suggested Mills helped orchestrate a cover-up that blamed a technical “glitch” in the White House archiving system that conveniently resulted in the loss of 1.8 million e-mails under subpoena in the Monica Lewinsky, Filegate and other scandal investigations.

Fast-forward to Hillary’s tenure as secretary. In October 2012, Mills sorted through key Benghazi documents and decided which to withhold from a review board. She also leaned on witnesses. Deputy ambassador to Libya Gregory Hicks testified before Congress in 2013 that Mills told him in an angry phone call to stop cooperating with investigators.

The FBI chief was fully aware of Mills’ M.O. when he launched his investigation. Yet even after discovering she was in the middle of everything improper, if not illegal, he treated her with kid gloves.

Comey knew it was Mills who had Hillary’s e-mails moved off her private unsecured server and onto laptops, where she decided which ones were government-related and OK for public release and which were “personal.” He knew it was Mills who shredded the e-mails that were printed out and who had the rest of the 31,000 e-mails deleted, and then had the laptops bleached clean.

And he knew it was Mills who told the Denver tech who maintained the server to stop retaining her e-mails and to delete Hillary’s archived e-mails, all of which the tech dutifully performed after Congress subpoenaed them and ordered them preserved.

Even so, Comey agreed to grant Mills immunity in exchange for her cooperation in the investigation. He also agreed to ground rules that left some lines of inquiry off-limits. When agents in April tried to pin her down on the procedures she used to search for Hillary’s e-mails under order, she and her lawyer stormed out of the room. So much for Comey’s cooperative witness.

Mills claimed such information was protected under “attorney-client privilege,” which is ridiculous. Mills was chief of staff for Hillary, not her lawyer, at the time Hillary was bypassing government security and squirreling away state secrets in her basement.

And even though Mills deleted the records after she left State and was supposedly acting as Hillary’s attorney then, privilege does not apply when a client seeks advice on how to commit a crime and the crime is committed.

Yet Comey’s agents abided by her claim and never pursued the line of questioning again. In effect, they gave her a pass on the whole question of the criminal obstruction behind which she looks to be the mastermind. And then, three months later, they let her sit in on Hillary’s interview even though Hillary was represented by attorney David Kendall!

Mills should be dragged before Congress to publicly answer questions the FBI refused to ask her. But she would just lie with impunity like she did in her past testimony involving other Hillary scandals.

Rather, it would be more productive to grill Comey under the klieg lights. Why did he give a key suspect who orchestrated the destruction of government records immunity as a witness? Why didn’t he demand prosecutors convene a grand jury to question Mills under oath? Was he pressured by the attorney general?

Sweating Mills could have cracked the case wide open. No one would have ever let H.R. Haldeman get away with editing the Nixon tapes. Why would the FBI director let Hillary’s chief of staff get away with deleting her e-mails?

Paul Sperry is author of “The Great American Bank Robbery,” which exposes the role of race-based Clinton housing policies in the mortgage bust.