Republican peculiarities in this political season are so numerous and lurid that insufficient attention is being paid to this: The probable Democratic nominee’s principal credential, her service as secretary of state, is undermined by a debacle of remarkable dishonesty.

Hillary Clinton’s supposedly supreme presidential qualification is not her public prominence, which is derivative from her marriage, or her unremarkable tenure in a similarly derivative Senate seat. Rather, her supposed credential is her foreign-policy mastery. Well.

She can’t be blamed for Vladimir Putin’s criminality or, therefore, for the failure of her “reset” with Russia, which was perhaps worth trying. She can’t be blamed for the many defects of the Iran nuclear agreement, which was a presidential obsession. And she can’t be primarily blamed for the calamities of Iraq, Syria and the Islamic State, which were incubated before her tenure.

Libya, however, was what is known in tennis as an “unforced error,” and Clinton was, with President Obama, its co-author.

On March 28, 2011, nine days after the seven-month attack on Libya began and 10 days after saying it would last “days, not weeks,” Obama gave the nation televised assurance that “the task that I assigned our forces [is] to protect the Libyan people from immediate danger and to establish a no-fly zone.”

He said US forces would play only a “supporting role” in what he called a “NATO-based” operation, although only eight of NATO’s 28 members participated: “Broadening our military mission to include regime change would be a mistake.”

Then-Defense Secretary Robert Gates said no vital US interest was at stake. Recently, he told The New York Times “the fiction was maintained” that the goal was to cripple Moammar Khadafy’s ability to attack other Libyans.

This was supposedly humanitarian imperialism implementing “R2P,” the “responsibility to protect.” Perhaps as many as — many numbers were bandied — 10,000 Libyans. R2P did not extend to protecting the estimated 200,000 Syrians that have been killed since 2011 by Bashar Assad’s tanks, artillery, bombers, barrel bombs and poison gas.

Writing for Foreign Policy online, Micah Zenko notes “just hours into the intervention, Tomahawk cruise missiles launched from a British submarine stationed in the Mediterranean Sea struck an administrative building in [Khadafy’s] Bab al-Azizia compound.” A senior military official insisted “[Khadafy’s] not on a targeting list.”

This was sophistry in the service of cynicism: For months, places he might be were on targeting lists.

The pretense was that this not-really-NATO operation, with the United States “supporting” it, was merely to enforce UN resolutions about protecting Libyans from Khadafy.

Zenko, however, argues that the coalition “actively chose not to enforce” the resolution prohibiting arms transfers to either side in the civil war.

While a senior NATO military official carefully said, “I have no information about” arms coming into Libya, and another carefully said that no violation of the arms embargo “has been reported,” Zenko writes that “Egypt and Qatar were shipping advanced weapons to rebel groups the whole time, with the blessing of the Obama administration.”

On May 24, 2011, NATO released a video showing sailors from a Canadian frigate, supposedly enforcing the arms embargo, boarding a rebel tugboat laden with arms. The video’s narrator says: “NATO decides not to impede the rebels and to let the tugboat proceed.” Zenko writes, “A NATO surface vessel stationed in the Mediterranean to enforce an arms embargo did exactly the opposite.”

On Oct. 20, 2011, Clinton was told insurgents, assisted by a US Predator drone, had caught and slaughtered Khadafy. She quipped: “We came, we saw, he died.” She later said that her words expressed “relief” that the mission “had achieved its end.”

Oh, so this military adventure was, after all, history’s most protracted and least surreptitious assassination. Regime change was deliberately accomplished, and Libyans are now living in the result — a failed state. If you seek her presidential credential, look there.