President-elect Donald Trump went on the Twitter warpath yesterday, blasting the intelligence community for allowing a Russian dossier with salacious claims about him to wind up in the hands of the media.

This was his rhetorical question: “Are we living in Nazi Germany?”

Actually, if I could choose a historical era that most evokes my fears, it would not be Germany, circa 1938 — however terrifying that period is.

It would be the Holy Roman Empire, about a thousand years before that.

Or, as the Hebrew-Yiddish poet Zalman Shneur wrote in 1913: “The Middle Ages are approaching.”

The Middle Ages are approaching — in the form of hatred of the Other, and in the form of anti-science rhetoric.

It is not only about climate change.  It is also about the denial of the validity and safety of vaccination.

Trump has asked Robert Kennedy Jr. to chair a new commission on vaccination.

RFK Jr. (who, as recently as August 2016, referred to Trump as “dangerous” and “a demagogue”) is vehemently anti-vaccination. He steadfastly supports the now-discredited theory that vaccination causes autism.

This has been RFK Jr.’s position for quite some time. In 2005, published both in Rolling Stone and Salon, he wrote an article claiming that thimerosal-containing vaccines caused autism. Salon retracted the article, in response to criticisms that it was inaccurate.

Once upon a time, conspiracy buffs limited their attention to the assassinations of RFK Jr.’s uncle and father.

Today, however, RFK Jr. focuses his conspiratorial paranoia on government health agencies that have “colluded with Big Pharma to hide the risks of thimerosal from the public.”

In fact, RFK biographer Jerry Oppenheimer suggests that RFK Jr.’s championing of the anti-vaccination message was probably responsible for his failure to be selected as head of the EPA under President Obama.

I find this all very sad. I had profound respect for the younger Kennedy’s father. And yet, RFK Jr.’s own story is complex. All too typical of this generation of Kennedys, it has been a combination of vast promise and vast disappointment.

But, here is what is even sadder.

I have often noted that right-wing rhetoric and left-wing rhetoric have a lot in common. That is certainly true of anti-Semitism and anti-Israelism.

It turns out that there is another intersection — conspiracy theories that traffic in the bizarre and unreasonable.

What does Judaism say about vaccination?

• To heal someone — or yourself — is a mitzvah (a religious obligation). Rabbi Abraham Joshua Heschel wrote: “Medicine is prayer in the form of a deed. The act of healing is the highest form of the imitation of God.”
• You’re not allowed to endanger yourself needlessly. The Shulchan Arukh, the classic code of Jewish law, says: “Wherever there is a potentially life-endangering pitfall or obstacle, it is a positive commandment to remove it, to be on guard against it and to take very good care in the matter, as the Torah says: “Guard yourself and guard your soul.” (Deuteronomy 4:9-10).

We are becoming sadly accustomed to conservative voices that are anti-science.

But, the liberal anti-vaccination people throw another piece into the conversation — teh typical modern assertion that “I have my rights, and no one can tell me what to do with my children.”

Here is a shocker.

Judaism does not believe in parental rights. It believes in parental responsibility.

The Talmud says Jewish parents are obligated to teach their children three things: Torah, a trade, and how to swim.

“Swimming” is a metaphor. Parents need to teach their children how to avoid dangerous situations.

Like, for example, infectious diseases.

That is why the “it’s my kid and I will do what I want to” argument is bogus. As a society, we are all in this together.

As Ben Boychuk, an associate editor of the Manhattan Institute’s City Journal, writes: “Your right to refuse to vaccinate your children ends where my children’s right to avoid needless exposure to infection begins.”

So, yes – we might be welcoming a new Middle Ages. When people reject science, when they rely on fear rather than facts, we are inching toward a medieval past.

That is the duty of all modern religious people: to name the coming tide of medievalism, and to fight against it.