After President Trump noted in March that an anti-malarial drug had shown some success in treating COVID-19, according to reports from clinicians, his opponents slammed him for playing doctor and flaunting the “audacity of false hope,” in the words of CNN’s Stephen Collinson.

How quickly they forget the lessons of the 1980s AIDS crisis.

Rachel Maddow demanded the media stop broadcasting Trump’s briefings, because “it’s misinformation.” The New Yorker called Trump’s interest in the efficacy of the drug, known as chloroquine, “quackery,” “eccentric,” “a ­reminder, if one was needed, of his scorn for rigorous science.”

USA Today, Vox, The Daily Beast, The Boston Globe, The Washington Post and NBC News all piled on. The governors of Nevada and Michigan issued ­decrees limiting doctors’ discretion to prescribe the drug; two former Food and Drug Administration chiefs are furious that chloroquine has been granted “emergency-use authorization,” bypassing FDA protocol.

Chloroquine is a venerable drug listed on the World Health Organization Model List of Essential Medicines. Doctors prescribe it millions of times annually for malaria, as well as for other “off-label” uses.

As Trump’s critics have rushed to point out, the drug has serious side effects — typically after being taken for years — but that’s no surprise. “The poison is the dose” is an ancient maxim in medicine; all powerful, useful drugs have to be administered carefully, and they usually have significant side effects.

It’s true that chloroquine is “untested” as a therapy for COVID-19, and that its possible successes are “anecdotal.” But how could it be otherwise? The virus and the disease are brand new. There are no tested, proved therapies for it.

What’s odd is that naysayers appear to have forgotten the ­major drug-approval battles over treatments for AIDS, a watershed in American gay history. Before the advent of the miraculous anti­retroviral medicines that have saved millions of lives, HIV was a death sentence. Like the novel coronavirus, it was a killer that came out of nowhere, and no one knew how to treat it as it ravaged its victims’ immune systems.

Groups like ACT UP accused the FDA under President Ronald Reagan of dragging its feet, with its insistence on lengthy, rigorous clinical tests for AZT, ribavirin, peptide-T and other drugs that appeared to have positive — though “anecdotal” — ­effects on AIDS patients.

Comparing AIDS to the Holocaust, with Reagan in the role of Hitler, ACT UP founder Larry Kramer and other activists likened the very same Dr. Anthony Fauci to Adolf Eichmann — the Nazi functionary who organized the trains to Auschwitz — because he was too cautious about expediting drug approval.

Reagan’s responsibility for deaths from AIDS is still a cherished myth on the left. When Hillary Clinton praised Nancy Reagan at her 2016 funeral, she was forced to apologize by the Human Rights Campaign, which considered revoking its endorsement of her candidacy.

The award-winning 2013 hit movie “Dallas Buyers Club” tells the story of a group of HIV-positive activists who, frustrated by FDA intractability, smuggled ­unapproved drugs from Mexico and sued the government to ­allow them to use them. Their desperation, and willingness to try untested medical protocols to save lives, was shown as heroic, not irresponsible.

Trump’s interest in the malaria drug as a coronavirus treatment didn’t come to him in a fever dream. Doctors in France, Malaysia and China conveyed positive outcomes, and anecdotal reports from clinicians in New York and other locales suggested that the drug had a salutary effect.

The New York state Department of Health, with the full support of Gov. Andrew Cuomo and backed by the Bill & Melinda Gates Foundation, is currently giving chloroquine to thousands of people suffering from COVID-19. And there are reports — indeed, anecdotal — that it can work.

The same people on the left who claim to “love science” don’t understand how it works. Science is an iterative, experiential practice of trial and error. Doctors make observations, try something, adjust, tweak dosages — and try again. That’s how ­every advance in medicine has always happened.

And remember that it was the same FDA bias toward following its own rules that led it to refuse to approve “unproved” coronavirus tests, delaying our responsiveness, and costing precious time.

Saying that there’s “no evidence” that chloroquine works is playing games with words. ­Responsible people are taking it seriously, and there appear to be positive reports about it. The ­reflexive Trump-haters should let this one go.

Seth Barron is associate editor of City Journal. Twitter: @SethBarronNYC