If you want to witness an adamantine mind at work, you could do a whole lot worse that observe the 44th president of the United States. Barack Obama is the most rigidly ideological president of my lifetime, a man who has a nearly blind adherence to a particular ideology (progressivism). It’s a disturbing, if at times a psychologically fascinating, thing to witness.

We’re seeing it play out in multiple ways, but let me offer just one illustration — his approach to jihadism. It has been clear from the start of his presidency that Mr. Obama has decided that Islam is wholly separate from Islamic terrorism, which explains his refusal to use the words (or variations of the words) radical or militant Islam. It also explains why his administration has used absurd euphemisms like “man-caused disaster” and “workplace violence” to describe Islam-inspired attacks. Why the 2009 Christmas Day bomber, Umar Farouk Abdulmutallab, was an “isolated extremist.” Why the shooting at a Kosher supermarket in Paris earlier this year was “random.” (The gunman had declared his allegiance to ISIS.) And why the president, in an effort to protect Islam, invokes the Crusades at a National Prayer Breakfast, despite the fact that the Crusades happened roughly a thousand years ago. On and on it goes.

We have a president who is eager to put a racial frame around incidents in which white cops kills blacks, even if, as in the case of Officer Darren Wilson and Michael Brown, the shooting was justified and there was no evidence that it was racially motivated. No matter; the incidents fit into Mr. Obama’s worldview, and off to the races he went.

But in the case of jihadism, when the killers themselves are invoking the Koran and the Islamic faith to justify their malevolence — when the caliphate established in the heart of the Middle East is called the Islamic State — the president refuses to confront it. He goes into contortions to downplay or ignore the connection to Islam. He has a narrative to advance, and he will do it even if he has to run roughshod over reality to do it.

No one is asking Mr. Obama to indict all of Islam or have America or the West declare a war on it. He should do neither. But what we should expect is the president to understand the nature of the enemy we’re facing. It would also be refreshing if the president did not live in a world hermetically sealed off from facts that are inconvenient to his worldview. But that is precisely what Mr. Obama is doing.

Barack Obama has a self-conceit: He sees himself as pragmatic, empirical, a man driven by reason rather than emotion, truth rather than dogma. Which simply underscores how ideological he is. His self-conception is a self-delusion; he is blind to how closed his mind is and how much he distorts reality in the cause of his meta-narratives. This happens on issue after issue — Mr. Obama’s intellectual distortions are not, alas, contained to a single topic — but it may be most pronounced in his utter inability to see the struggle within Islam that is unfolding before his very eyes. He doesn’t want it to be true, and so he won’t allow it to be true.

Here’s the problem: There is an independent reality apart from what Mr. Obama thinks. He can ignore the truth, but he cannot wish it out of existence. And by ignoring the reality of things, he makes everything worse. (It turns out that calling ISIS a “jayvee team” last year and declaring it “contained” a day before the massacre in Paris doesn’t make it so. Who knew?)

Mr. Obama is lost and confused, inhabiting a world of his own making. That would be bad enough if he was a community organizer; it is disastrous for a man who is president. America and the world are paying a terrible price because of the closing of Barack Obama’s mind.

Peter Wehner is a senior fellow at the Ethics and Public Policy Center.