Despite his role as the key player in the late, unlamented fool’s errand known as the Iraq War, former Defense Secretary Donald Rumsfeld has remained the most elusive of subjects. A big part of this has to do with him not meeting our expectations, or in any event my own: He remains unapologetic, unrepentant and unconscionably obtuse when it comes to discussing the war, notably the chief rationale for starting it — that Saddam Hussein possessed weapons of mass destruction — which of course was discredited almost from the start.

Errol Morris has now penetrated Rumsfeld’s armor (which he compares to a turtle’s carapace) in a four-part New York Times op-ed series based on his interviews for The Unknown Known, a 2013 documentary in which Rumsfeld discusses his career from his days as a congressman in the early 1960s to the invasion of Iraq in 2003.

I happen to think the Times series is way too long, and spare me the copious footnotes, okay? But I slogged through the entire series with the (it turns out) prescient feeling it all had an Alice in Wonderland quality about it, and was rewarded with these closing observations by Morris in the fourth part:

“The history of the Iraq war is replete with false assumptions, misinterpreted evidence, errors in judgment. Mistakes can be made. We all make them. But Rumsfeld created a climate where mistakes could be made with little or no way to correct them. Basic questions about evidence for W.M.D. were replaced with equivocations and obfuscations. A hall of mirrors. An infinite regress to nowhere. What do I know I know? What do I know I know I know? What do I know I don’t know I don’t know? Ad infinitum. Absence of evidence could be evidence of absence or evidence of presence. Take your pick. An obscurantist’s dream.

“There’s a quotation I have never liked. It comes from F. Scott Fitzgerald’s The Crack-Up. ‘The test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function.’ Not really. The test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time and know they are opposed.

“People embrace contradictory positions, often without being aware of it. Sometimes not caring. Sometimes proud of it. Rumsfeld seems (with pleasure) to say ‘p’ and ‘not-p.’ What he would call the two sides of the coin. One side: ‘If you wish for peace, prepare for war.’ The other side, ‘Belief in the inevitability of conflict can become one of its main causes.’ Not exactly a contradiction. But where does he stand? His follow-up: ‘All generalizations are false, including this one’ — doesn’t clarify much of anything.

“When asked how Colin Powell could have presented such shoddy evidence for W.M.D. in Iraq to the United Nations, Rumsfeld told me, ‘ . . . because he believed it.’ Fine, as far as it goes. My guess is Rumsfeld is right. When Powell appeared before the United Nations on Feb. 5, 2003, he believed what he was saying. . . .

“Rumsfeld, too, may believe what he is saying. But believing something does not make it true. The question is why he believed what he believed. On the basis of what evidence? Mere belief is not enough.

“In Lewis Carroll’s Alice in Wonderland, Alice, perplexed by her encounter with the Cheshire Cat, says, ‘I have seen a cat without a grin, but I have never seen a grin without a cat.’ I had a similar experience with Donald Rumsfeld — his grin and my puzzlement about what it might mean. I was left with the frightening suspicion that the grin might not be hiding anything. It was a grin of supreme self-satisfaction and behind the grin might be nothing at all.”

History already has judged Rumsfeld’s stewardship harshly, and he certainly was the worst defense secretary since Robert McNamara, who served under Presidents Kennedy and Johnson. McNamara, in turn, was the worst since Jefferson Davis, who as secretary of war under Franklin Pierce worked tirelessly for Southern interests and was instrumental in helping push the U.S. toward civil war.

In fact, Rumsfeld was the worst hands down.

Like Rumsfeld, McNamara was a control freak who thought he had all the answers, lacked the crucial element of common sense and surrounded himself with sycophantic acolytes. Like Rumsfeld, he presided over an unpopular war built on a foundation of false assumptions and outright lies. Like Rumseld, there was an amorality to his actions. And like Rumsfeld, he squandered the respect of his generals and admirals.

But without McNamara, there still would have been a Vietnam War, while there would not have been an Iraq war without Rumsfeld.