More than a week later, America is still struggling to understand what produced last Tuesday’s election stunner, but here’s one factor that’s too little discussed: Hillary Clinton’s relentless (and in my view, accurate) attacks on Donald Trump’s character may actually have made his supporters more entrenched.

One of my closest high school friends drove home this point in a message two days after the vote. “As a traditional Christian, I felt attacked, myself — not implicitly, but explicitly — during the entire election cycle,” he emailed me. The attacks on Trump by Clinton and the media backfired, he argued.

I’ll come back to my friend’s comments in a moment, but first some background.

This “backfire effect” was something I explored in a column in August. I cited behavioral science research by Christopher Graves, global chairman of Ogilvy Public Relations, and others showing that attempts to refute false information could actually reinforce people’s misperceptions.

“Arguing the facts doesn’t help ­ in fact, it makes the situation worse,” Graves had written in February 2015 in the Harvard Business Review. Because of a behavioral trait known as “confirmation bias,” people discount arguments that challenge their beliefs. “Instead of changing their minds, most will dig in their heels and cling even more firmly to their originally held views.”

If this psychological research is accurate, then the Clinton campaign’s focus on Trump’s racist and sexist statements may have had the perverse effect of making his supporters feel defensive, and more supportive. That was especially true after Clinton called some holding these views a “basket of deplorables” (and again, I thought she was right to admonish them).

Graves noted in an October interview with the Harvard Business Review: “Clinton’s categorization of Trump’s supporters as deplorable is an example of what behavioral scientists call ‘outgroup derogation.’ It can be a powerful mobilizing ­ and polarizing force.” People who feel attacked retreat to “which tribe we hope to be identified with, and which we would not want to be caught dead with.”

Now, back to my high school classmate, the Rev. Paul F.M. Zahl. He was the top student at my school, graduated from Harvard University and took a doctorate in theology from the University of Tubingen (in Germany). He’s not the stereotypical undereducated Trump voter, in other words. He has been dean of an Episcopal cathedral, head of a seminary and rector of local parish churches. My friend’s email continues:

“I told some friends, 18 months ago, that I believed Trump would win, even though I did not expect to vote for him — for the simple reason that what you resist, persists.” Zahl cited a passage from Scripture to support his argument: “‘The Law increaseth the trespass'” — which is to say, the more one interdicts a phenomenon, the more reaction among those who identify with the phenomenon.”

Zahl went further, taking me and my colleagues to task: “The media, in my opinion, helped make this happen — albeit, unwittingly. I felt personally attacked by the Democratic Party’s current ethos, as a Bible Christian. I wondered whether, if Clinton won, I and others who believe as I do would be considered legitimate Americans anymore.”

I wrote back to my friend (with whom I have been having political arguments for 55 years):

“Dear Paul: In friendship and respect: This notion that ‘the media made me do it’ baffles me, frankly. Each human brain (and heart) must weigh these choices, yes, prayerfully, in terms of what is best for the country. Sixty-three percent of those voting thought Trump was unqualified, 61 percent thought he was temperamentally unsuited to be president, according to exit polls. Yet people voted for him anyway, out of … what? Spite? Anger at the media? I see what has happened, and it makes me very sad, but each voter is responsible for making a wise decision, no?”

And Zahl responded: “No, David. Many people don’t make decisions rationally or even consciously. … When people are told, across the board, that they are ‘xenophobes, racists, misogynists, and Islamophobes’ for holding the views they do — whatever they are — they become hardened in those views.

“Condemnation (of people or groups of people — and this goes for all ideologies, right and left) always has the opposite effect: ‘The Law (i.e., judgment/condemnation) increases sin (i.e., the very thing that the judgment is supposed to correct or educate),'” Zahl admonished.

We’re all working through the meaning of this election with our family and friends. Zahl urged me to share his thoughts with readers. Amen to that.

Let’s keep talking.

— David Ignatius is a columnist for Washington Post Writers Group.