Now that Trump has finally turned to the campaign promise that won him the election — build a wall and deport illegals — the Democrats, the media and even most Republicans are hysterical.

Just remember: They were hysterical about Ronald Reagan, too. You don’t change history by being a follower, particularly if the people you’re following are unimaginative, go-with-the-flow company men.

When President Reagan implemented the strategy that won the Cold War, he was opposed by the entire media, as well as foreign policy “experts” in both parties.

The New York Times and Washington Post produced nonstop denunciations of his “dangerous” policies. There were propaganda movies like “The Day After,” terrifying Americans about a Soviet strike on our country. Witless college students demanded cyanide pills be stocked in campus health care clinics, on the grounds that Reagan was going to get us all nuked.

Only after Reagan’s policies succeeded did these same hysterics say, Ho hum, no big deal. We always knew the Soviet Union was a paper tiger.

Frantically rewriting history, they claimed Reagan had merely continued the policies of his predecessors. The truth about their eight-year primal scream is helpfully assembled in my smash best-seller, Treason: Liberal Treachery from the Cold War to the War on Terrorism.

The Democrats, the media and most of the Republican Party are as fanatically opposed to Trump’s ideas about illegal immigration as they were to Reagan’s ideas about winning the Cold War.

Like Reagan, Trump has only the people on his side. Unlike Reagan, he doesn’t seem as confident that he is right.

So the people need to be louder.

All we’re getting from the media on immigration is an avalanche of lies, neurotically repeated by people citing one another:

Polls show Americans don’t want a wall!

We’re a nation of immigrants!

Immigrants commit less crime than the native born!

Studies show: Black Americans are NOT hurt by illegal immigration.

Every one of these claims is a lie, as demonstrated in my book Adios, America. (Also a smash best-seller.)

People assume a minimal standard of decency in others and think to themselves, Well, Joe Scarborough wouldn’t say that if it weren’t true.

What viewers don’t understand is how lazy media personalities are. They are merely quoting what someone told them. They don’t know. Their expertise consists of memorizing a set of talking points, like ABBA memorizing the syllables to English words without knowing what they meant.

If journalists allowed follow-up questions and you could ask, “How do you know that?” The answer would be, “I heard it from a guy at Vox.”

The media go to extremely biased sources; they know nothing, so they’re not in a position to challenge them; and even if they were, they wouldn’t, because they’re on the same team.

After a New York Times reporter tracked me down for a quote about the wall, I gave him the following, but he chose not to run it. Why should the Newspaper of Record present the opposition’s side honestly?

There are a million reasons we want a wall, but here are five:

1) The Simpson-Mazzoli Act — passed almost 30 years ago to the day Trump was elected president — came with elaborate promises that it would put an end to illegal immigration. In fact, 30 to 40 million more illegals have poured into our country since then.

2) Notwithstanding the vast number of illegal alien valedictorians, there are also criminals, drunk drivers, drug cartel members and desperately poor people consuming government services meant for the least among us and driving down the wages of our working class.

3) We need a better method.

4) Walls work. See Israel.

5) If we don’t get it done now, we never will. Trump is our last chance.

But instead of explaining to the Times’ readers why Trump’s promise to build a wall shook the political world to its foundation, the newspaper trotted out campaign adviser Sam Nunberg’s boast that he invented “build the wall” because Trump’s mind tends to wander. It was only a dumb talking point, you see, not a serious campaign pledge.

This is like claiming you were the guy who invented carrying an umbrella when it rains. I’m sorry, Sam, but you’re not getting royalties for that.

Building a wall is kind of an obvious idea for protecting a border. Not only have walls been used from time immemorial to defend borders, but those precise three words have been used to describe what should happen at our specific border thousands of times before Trump used them, according to a quick Nexis search.

The current DNC talking point against a wall is that it is a “medieval solution to a 21st-century problem!” Turn on MSNBC or CNN right now, and you’ll hear someone saying it.

So are wheels. Are Democrats taking tires off their cars?

A roof is a medieval solution. How about Nancy Pelosi replace the one over her house with “new technology” — like a drone! Drones won’t keep anything out, but at least she can see what’s coming in seconds before it drops on her head.

Medievalism: 1; Pelosi: 0.