Anti-vaxxers think they finally have a friend in the White House. Donald Trump has voiced concerns about vaccines for at least a decade, and, in August, he reportedly attended a fundraiser with disgraced and delicensed doctor Andrew Wakefield, whose discredited research helped launch the anti-vaccination panic.

But Trump isn’t quite an anti-vaxxer. If he were, he wouldn’t have vaccinated his own children. In fact, Trump is a slow vaxxer, which means he accepts the idea of vaccination, but he thinks kids get too many vaccines, too early in life. In practice, this means parents pick their own vaccine schedule, scientific standards be damned.

If you are struggling to understand the appeal of Donald Trump—as I have been for months—his vaccine position offers a window. Trump occupies a middle ground between fact and fiction. For people who can’t distinguish between the two, this compromise is irresistible.

Imagine that you don’t understand medical research. You’re torn between the medical establishment and the scary claims of anti-vaxxers. In that context, slow vaxxing seems like the ideal third way. Here’s Trump, talking about his son Baron in 2007.

[W]e’ve taken him on a very slow process. He gets one shot at a time then we wait a few months and give him another shot, the old-fashioned way. But today they pump the children with so much at a very young age. We do it on a very, very conservative level.

What could be more reasonable? Slow. Old-fashioned. Not just conservative—very, very conservative.

Also, relatable.

“Trump’s statements on vaccines reflect what a lot of people think,” says Daniel Salmon, deputy director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health.* “In surveys, between one-quarter and one-third of parents say we give too many vaccines.”

Trump has staked out a centrist position, smack dab between scientific fact and total bullshit. It’s his signature move on scientific issues like climate change.

But mixing one part fact with one part fiction does not get you something that is partially true. Those who understand the science know that everything Trump says about vaccines is wrong.

For one thing, slow vaxxing is not actually old-fashioned. The old-fashioned way to vaccinate was quite the opposite: We used to wallop a child with an enormous dose of antigens all at once. The smallpox vaccine that Trump likely received as an infant required his immune system to respond to 200 different proteins. Today the entire compliment of child vaccines contains just 160 proteins. Children do receive 10 times more shots today than they did a century ago, but the number of needle sticks is irrelevant—it’s the size of the immune challenge that matters. Of course, you need some scientific literacy to understand this difference.

Furthermore, Trump’s claim that we “pump children with so much at a very young age” reflects a widely held concern that the current vaccine schedule can overwhelm a child’s immune system. This is nonsense. Yes, a vaccine exposes a child to a very small amount of a virus. Conservative estimates suggest that the infant immune system could likely respond to more than 10,000 vaccines in a single doctor’s visit. Put differently, vaccines occupy about 0.1 percent of an infant’s immune capacity. A baby encounters more microbes on its trip through the birth canal than from vaccines.

Trump’s most dangerous claim is that slow vaxxing is “conservative.” Conservatism is about avoiding unnecessary risk. But delaying vaccination introduces a lot of unnecessary risk.

“If you get pertussis as an infant, it’s potentially deadly,” notes Salmon. “If you get it as an adolescent, it’s usually a prolonged cough.”

This is one of the primary factors guiding the current vaccine schedule, Salmon explains. We give vaccines to children when they most need them. Delaying vaccination is not conservative—it’s ignoring the evidence.

The only conservative aspect of the slow-vaxx approach is its appeal to our moderation bias, or, roughly, our preference for compromise (one of the only biases you wouldn’t have expected Donald Trump to harbor). There’s no need to moderate with vaccines, though. The Advisory Committee on Immunization Practices, the Centers for Disease Control committee that establishes the recommended vaccine schedule, has already done the moderating for you. Before any vaccine is added to the schedule or moved, ACIP reviews a mountain of data on the possibility of interactions with other vaccines. New vaccine trials involve tens of thousands of patients—far more than most medical trials. So altering the vaccine schedule is like reaching into a finely tuned engine and randomly moving the parts around.

Trump adopted a delayed vaccine schedule in 2007, the same year Robert Sears (son of well-known pediatrician William Sears) published The Vaccine Book: Making the Right Decision For Your Child. Citing baseless concerns about vaccine safety, the younger Sears proposed “Dr. Bob’s Alternative Vaccine Schedule,” which unfortunately took off.

“The CDC researches the interactions of every vaccine on its schedule,” says Paul Offit, a professor of pediatrics in the division of infectious diseases at Children’s Hospital of Philadelphia. “Dr. Bob just sat in his office and made up his own schedule—two pages at the back of his book. Parents would copy it and pass it around. It was unnecessary and dangerous.”

Few slow vaxxers follow Dr. Bob’s schedule to the letter. But intentionally or otherwise, Dr. Bob gave parents license to make up whatever vaccine schedule pleased them. (If Dr. Bob can do it, so can you.) Between 2003 and 2009, the proportion of parents who delay vaccines nearly doubled to 40 percent. (Most of those parents don’t adhere to Dr. Bob’s delayed schedule.) Vaccine scheduling is now DIY.

Even the most strident defenders of the medical establishment understand the motivations for vaccine delay: It’s hard watching your baby injected with more than a dozen foreign biological agents. It’s also easy to tell yourself that the risk of contracting a vaccine-preventable disease is low. In fact, the risk is low. But that doesn’t mean it doesn’t happen and that they’re not dangerous.

“Not a year has gone by that I don’t see a child in our hospital with a vaccine-preventable disease—not once in 15 years.” says Offit. “The risk for each individual is still low. But even if there are 999 empty chambers, you shouldn’t play Russian roulette with your child.”

With Trump, it always comes back to Russia.

*Correction, Jan. 11, 2017: This story originally misidentified Daniel Salmon as the director of the Institute for Vaccine Safety. He is the deputy director. (Return.)