What about Vice President Biden? That’s the question that begs to be asked while the Democratic press pursues its campaign to get General James Mattis to turn publicly against the president he served as Secretary of Defense. What does the legendary Marine think of the former veep who is now the frontrunner for the Democratic nomination for president.

Not much, it turns out. We know that because in his new book, “Call Sign Chaos,” the general minces no words in respect of Mr. Biden. He suggests that in the thick of the fight in Iraq, the former chairman of the Senate Foreign Relations Committee was a weak reed. He puts the particulars to Governor Sarah Palin’s famous jibe, in the 2008 election debate, that Mr. Biden was waving the “white flag of surrender.”

It’s not that anyone gainsays Mr. Biden’s attention to Iraq. He often boasts, and fair enough, of his dozens of trips to the fronts in the Middle East and Afghanistan. It’s his jackleg judgment. We glimpse it in General Mattis’s account of the late summer of 2010, when the general, then head of CentCom, flew to Baghdad for the change of command when General Lloyd Austin took over from General Ray Ordierno.

General Ordierno, in General Mattis’s telling, had given Mr. Obama’s defense secretary, Robert Gates, “a carefully calculated plan to leave a residual force of eighteen thousand troops.” So when the generals met Mr. Biden privately in Iraq, the key issue was who would be the next Iraqi prime minister and “how would that choice affect U.S. troop withdrawals and stability inside the country?”

President Obama, General Mattis relates, “had said we would maintain a residual force ‘to advise and assist’ the Iraqis.” The generals “assumed this would be a sufficient number to hold the gains we had achieved at great cost, a number we’d reduce as Iraqi capabilities increased.” So after the change of command ceremony, the American ambassador, Jim Jeffrey, invited the generals to dinner with the visiting vice president.

At the dinner, General Mattis warned bluntly of Prime Minister Nouri al-Maliki. General Mattis called him “highly untrustworthy,” aiming to “purge or marginalize” Sunnis and Kurds from the government. “He’s devious when he talks to us,” General Mattis relates telling Mr. Biden. Mainly, though, he stressed the importance of keeping a residual force of American troops in Iraq.

“I was thinking of the training wheels on a bicycle: We shouldn’t suddenly pull off those wheels,” General Mattis writes in his new book. He adds: “While political considerations rightly guide strategic decisions, political decisions are unsustainable when they deny military reality. Properly aligned, political considerations and strategic decisions are the keys to a better peace.”

What is so shocking about General Mattis’s account is Vice President Biden’s reaction. He “listened politely,” the general writes. It was, though, “like talking to people who lived in wooden houses but saw no need for a fire department.” It was apparent that “the die was already cast.” The general writes that the realization that our diplomats were outside of the policy-making loop left him “dumbfounded.”

“Know why you’re at CentCom?” Mr. Biden teased the future Secretary of Defense. “Because no one else was dumb enough to take the job.” The general reckoned he was “an admirable and amiable man” but “past the point where he was willing to entertain a ‘good idea.’ He didn’t want to hear more; he wanted our forces out of Iraq. Whatever path led there fastest, he favored.”

In the event, the Obama-Biden team “ended” the war in Iraq, just as they had promised. The result was a tragedy, just as General Mattis had warned. “It was like watching a car wreck in slow motion,” he writes in his new book. Into the vacuum, ISIS arose “like a phoenix,” establishing its “murderous caliphate” with its “untold misery for millions of innocents.”

Which brings us back to Sarah Palin. That’s exactly what the alert Alaskan, as we like to call her, was talking about when she warned that Mr. Biden was waving the white flag of surrender. Even President Trump, who insists he opposed the war in Iraq at the start, opposed such a reckless retreat at the end. He wanted to finish the job we’d started — which, in our view, is a far better strategy than that of the Democrats’ front-runner.