“Rarely has a president changed his party as fast and profoundly as Donald J. Trump. Love him or hate him, you can no longer argue his ability to bend an entire party to his will,” writes Axios’ Jonathan Swan in a piece titled “The cult of Trump.”

A source “close to GOP leadership” tells Mr. Swan: “We’re all MAGAs now.”

I’m not quite sure it’s MAGA hats for as far as the eye can see, but Mr. Swan is right about the broader point. There has been a sea change on the right with Mr. Trump at the helm. And not just for HMS Grand Old Party.

To anyone who hasn’t lived and breathed in conservative circles, this change is both shocking and hard to comprehend. I agree it’s shocking, but it’s not so hard to comprehend.

Three distinct factors go a long way to explain it.

First, never before in modern American history have we had a president so transparently demanding not just of loyalty but praise from his subordinates and political allies. He considers criticism of his behavior a greater offense than voting against his agenda — and so do his most ardent supporters. This creates a powerful cultural incentive to define norms down, or just defenestrate them entirely.

This is one reason why evangelical leaders such as Jerry Falwell Jr., who have spent a lifetime talking about eternal principles, feel enormous pressure from above and below to give the president a “mulligan” on personal shortcomings (in the words of Family Research Council President Tony Perkins).

The other two factors say more about the rest of us than they do about Mr. Trump. One is the tribal belief that the other party is an existential enemy that will do anything. And so we must be just as ruthless.

All of that stuff about Mr. Trump being a “fighter” who “counterpunches” and isn’t “politically correct” is shorthand for this argument. But this attitude is not new to the GOP, nor to our politics generally. Under George W. Bush, one heard a great deal from the left about how only “fighting Dems” who refused to be intimidated could “take back America,” a slogan used by many Democratic politicians in the 2000s.

The dynamic only gets worse with each election. The party out of power convinces itself that obstruction — or now “resistance” — is the only option. The party in power talks a big game about bipartisanship, but it not only knows the other side won’t cooperate, it also realizes that its base sees compromise as weakness and capitulation.

The result is that the party in power races to get its agenda accomplished, and the base forgives any abuses or violations of norms in the process, thus proving the worst suspicions of the opposition.

Liberals roll their eyes at the claim that President Barack Obama violated democratic norms or abused his power. But putting aside the specific arguments, conservatives saw plenty of abuses and violations, from the IRS scandals and Benghazi to the Iran deal. Mr. Obama said many times he couldn’t unilaterally implement the Deferred Action for Childhood Arrivals program because he wasn’t a “king.” Then he did it anyway.

And the process repeats itself, getting worse and more egregious each time. When I criticize Mr. Trump, the first response from countless Republicans is, “Oh yeah, why was it OK for Obama!?” If I point out it wasn’t and that I said as much, they switch gears to how we need a fighter who gets things done and doesn’t care about the “old rules.”

Which brings me to the third factor.

Yes, there is a cult of Trump. But that’s because we have a cult of the presidency in this country. It infects not just our understanding of the office, but of the person holding it. When Mr. Obama acted like a king — by his own definition — liberals cheered, because their loyalty was to the man, not the office. It’s getting worse with Mr. Trump, but this dynamic has been getting worse for decades. And I suspect it won’t improve much when he’s gone.

Jonah Goldberg is a fellow at the American Enterprise Institute and a senior editor of National Review. His email is goldbergcolumn@gmail.com. Twitter: @JonahNRO.