Gen. David Petreaus lost his sterling reputation — and his job — last week. The blockbuster news of the CIA director’s resignation over an extramarital affair wasn’t just stunning. It was depressing.

Gen. Petraeus is the widely admired architect of the bold 2007 U.S. “surge” against opposition forces in Iraq. That hastened the end of America’s military involvement in Iraq, gave that nation’s long-suffering people a fair chance to govern themselves and rightly re-confirmed the general as a renowned expert in counterinsurgency warfare.

Back when he was a senator, Barack Obama criticized the surge plan crafted by Gen. Petraeus and approved by President George W. Bush. But as president, Mr. Obama picked the general to lead our mission in Afghanistan. And at President Obama’s request, Gen. Petraeus retired from the Army 14 months ago to become CIA director.

How could such a distinguished American, serving in an office where security is such a prime priority, be so reckless?

That’s just one of the troubling questions raised by Gen. Petraeus’ disgrace. Numerous federal lawmakers are fairly asking why the FBI waited months to inform the heads of congressional intelligence committee about the investigation that uncovered the affair. As one of them put it on “Fox News Sunday”:

“We received no advance notice. It was like a lightning bolt.”

That wasn’t a Republican senator still serving post-election sour grapes. That was freshly re-elected Democrat Dianne Feinstein, chair of the Senate Intelligence Committee.

She also said Sunday of the scandal: “That could have had an effect on national security. I think we should have been told.”

The alleged behavior of Gen. Petraeus’ mistress, Paula Broadwell, intensifies security concerns. She wrote a glowing biography of Gen. Petraeus and had classified information in her computer — though she contends she didn’t get it from him. The FBI discovered the affair only after Mrs. Broadwell sent threatening emails to another woman she suspected of having romantic designs on the general — though he and that woman insist that they were and are merely friends.

Other unanswered questions: Why were repeated signs of danger so tragically ignored before the Sept. 11 terror attack that killed Ambassador Christopher Stevens and three other Americans in Benghazi, Libya?

Why did the president, Ambassador to the United Nations Susan Rice and other Obama administration officials stick for so long to the absurd premise that the murderous Benghazi assault was not a planned terror attack but the result of a spontaneous protest against a video ridiculing Mohammed?

Sen. Feinstein cited “five prior incidents” in Libya this year. She correctly stressed that they “aren’t intelligence, they are not threats, they are actual attacks on the British ambassador, on our consulate once before, on a number of other things, on the United States missions.”

The Benghazi outrage happened on Gen. Petraeus’ CIA watch. Yet while he was initially scheduled to testify Thursday before the Senate and House intelligence committees, now that he has resigned, the agency intends to send Acting Director Michael Morrell in his stead.

That won’t suffice. Sen. Lindsey Graham, R-S.C., put it well Sunday on CBS’ “Face the Nation”: “I don’t see how in the world you can find out what happened in Benghazi before, during, and after the attack if General Petraeus doesn’t testify.”

At least Gen. Petraeus’ downfall, while an awful end to an impressive career in public service, delivers this reassuring reminder: The quaint notion of individual responsibility isn’t quite obsolete.

Lest you dismiss the general’s affair as a purely personal matter, review the Code of Federal Regulations’ logical identification of sexual misconduct as a security concern. It removes security clearances for “personal conduct or concealment of information that may increase an individual’s vulnerability to coercion, exploitation, or duress, such as engaging in activities which, if known, may affect the person’s personal, professional, or community standing or render the person susceptible to blackmail.”

A relatively recent president even issued an order toughening that regulation, adding that access to classified material requires a record of “strength of character, truthfulness, honesty, reliability, discretion and sound judgment, as well as freedom from conflicting allegiances and potential for coercion.”

That directive was signed in 1995 by President Bill Clinton.

And regardless of the irony in that particular presidential edict, our nation deserves a fuller accounting of what happened to Gen. Petraeus — and what happened in Benghazi.