War is peace. Freedom is slavery. Ignorance is strength. Truth isn’t truth.

Rudy Giuliani’s latest bon mot is a reminder, if anyone needed it, that calling the Trump administration Orwellian isn’t hyperbole, it’s just a statement of fact. Like the ruling party in “1984,” Donald Trump operates on the principle that truth — whether it involves inauguration crowd sizes, immigrant crime or economic performance — is what he says it is. And that truth can change at a moment’s notice.

For example, not long ago, Republicans insisted that Russia was our greatest threat, and that Barack Obama was betraying America by not confronting Vladimir Putin more forcefully; now Putin is one of the good guys, and the base has gone along with the change. We have always been at war with Eastasia.

And if you thought you heard something different from the Trumpian version of reality, blame evil conspirators and saboteurs, whom you get to denounce in the Two Minutes Hate, chanting “lock her up.”

But how did this happen to the whole Republican Party? And it is effectively the whole party: There is no serious G.O.P. opposition to Trump or his vision. Why did the party’s belief in objective reality collapse so suddenly and completely?

I don’t claim to understand the whole story. But one thing is clear: The Orwellification of the G.O.P. didn’t start with Trump. On the contrary, the party has been moving in that direction for years; the mind-set Trump is exploiting was already well in place before he burst on the scene.

Consider the claims of Trump and his allies that evidence of his collusion with Russia — not “alleged” collusion, because there is no longer any real doubt — is a hoax perpetrated by the “deep state.” Where have we seen something like that before? In Republican attacks on the evidence for climate change

Fifteen years have passed since Senator James Inhofe suggested that global warming is “the greatest hoax ever perpetrated on the American people.” This was and is an even crazier claim than the assertion of Trump and company that all of the tweeter in chief’s woes are the product of a vast deep-state conspiracy; it’s not far short of Pizzagate or QAnon territory. To take it seriously you have to believe in a vast international conspiracy involving thousands of scientists, not one of whom dares speak out.

Yet this paranoid fantasy has in effect become the official position of the G.O.P. Climate change deniers have pretty much given up on arguing about the evidence, although the old line “it’s a cold day, so global warming is a myth” still pops up now and then. Instead, it’s all about the supposed conspiracy.

What’s the evidence for this conspiracy? A lot of the argument rests on things like out-of-context quotes from stolen emails (sound familiar?), such as those sent among researchers at the University of East Anglia’s Climate Research Unit. Like the texts between two F.B.I. officials that supposedly prove the existence of a plot against Trump, “Climategate” actually showed nothing more than that the people involved were human. But to a determined conspiracy theorist, everything is evidence of nefarious activity.

And there’s more. Some people seem startled at how quickly Trump has moved to use the power of office to punish and intimidate anyone who doesn’t go along with Dear Leader. But Republicans have long been doing that on climate.

Most famously, Ken Cuccinelli, the former attorney general of Virginia, spent several years trying to prove fraud on the part of Michael Mann, one of our leading climate researchers. Cuccinelli’s witch hunt (yes, this was the real thing) was thinly disguised as involving concern over misuse of state funds, but it was obviously an attempt to use political power to censor and suppress inconvenient science.

And where were the Republicans standing up against conspiracy theories and for scientific integrity? Inaudible and invisible.

In short, if you followed the evolution of the G.O.P.’s position on climate change (not that Republicans believe in evolution, either), you shouldn’t be surprised at the party’s intellectual and moral collapse under Trump. For Republicans, ignorance has been strength for a long time.

There’s also, I believe, an additional relevant lesson from the climate story: the special rage of those who knowingly act in bad faith.

Climate denial is a deeply cynical enterprise; the people misrepresenting evidence and sifting through emails for “gotcha” quotes have to know that they’re not being honest. Yet their rage against “elitists” who continue to point out inconvenient truths is very real — because it’s a fact of life that many people feel special hatred for those they’ve mistreated.

The same goes for Trump and company. Trump knows perfectly well that he’s guilty of collusion. That doesn’t mean he’s faking his volcanic rage at those documenting his guilt: He hates his pursuers all the more because he knows they’re on the right track.

And as he lashes out, with no regard for law or the Constitution, will other Republicans try to hold him back? All the evidence suggests that they won’t.