You have probably heard by now that President Obama returned the salute of his security guards with a cup of coffee in his hand. And, depending on your political orientation, you see this as either further evidence of Obama’s disrespect for all that America stands for, or as a trumped-up non-controversy fanned by Obama-deranged Neanderthals just looking to discredit the president.

And then there is the whole double standard thing. Liberals quickly uncovered a picture of George W. Bush saluting with a dog—evidence that Obama’s critics don’t care about the salute as much as they care about criticizing anything that the President does. As Jon Stewart put it in a critique of Sean Hannity, “You are just trying to score points in a game that no one else is playing.”

written about before: the fact that human beings are much better at building narratives than we are at thinking critically, so once we have constructed a narrative about a person or event, we aggressively interpolate everything we encounter into the narrative we have already built.

In the narratives of many on the right, Barack Obama is a president who does not respect the military or take the protocols and traditions of the United States seriously. So when he makes a lazy salute, or wears a tan suit, or otherwise appears unserious about anything, people say “there he goes again” and interpolate the new evidence into the stories they have been telling for years.

It does not matter that Bush saluted with a dog, or that Reagan wore tan suits, because those presidents were generally perceived as ultra-patriotic. There was no existing narrative to interpolate new facts into. But that does not mean that they did not suffer from judgments based on confirmation bias. They did—just about different things.

Take George W. Bush. The narrative on the left was that he was unintelligent and uncurious—too dumb, even, to be the President of the United States. This meant that every time he made a verbal gaffe in public (and everybody eventually makes verbal gaffes in public), people said, “there he goes again. . . .”

Consider this speech in which Bush said, “rarely is the question asked are . . . is . . . ‘are children learning?’” He misspoke and corrected himself in a way that President Obama and every other public speaker sometimes does. But his political opponents seized on this, represented it as “is our children learning,” and maintained that the President of the United States didn’t know how to conjugate “to be.” Paul Begala even wrote a book about it.

So, certainly, George W. Bush could salute with a dog and not be criticized because very few people had a pre-existing narrative of him disrespecting the military. Similarly, Barack Obama, who is generally perceived as an intelligent person and a good speaker, could mix up “is” and “are” in a speech without half of the country thinking that he didn’t know how to talk.

That’s how the confirmation bias works. It is deeply wired into core elements of human cognition. This is (and always has been) bad news for the political discourse because it means that evidence, facts, data and the like will rarely influence anybody’s political opinions, which are based almost entirely on pre-existing narratives that are strong enough to accommodate almost any fact they encounter. We all pretty much prefer to believe that which we already know to be true.