Harry may not be a full-on patronus against the presumptive Republican presidential nominee’s appeal, but reading Potter stories does appear to be a shield charm against Trump’s message.

A new study to be published in a special 2016 election issue of PS: Political Science and Politics finds that reading Harry Potter books leads Americans to take a lower opinion of Donald Trump. In fact, the more books the participants read, the greater the effect.

Even when controlling for party identification, gender, education level, age, evangelical self-identification, and social dominance orientation — all factors known to predict Americans’ attitudes toward Donald Trump — the Harry Potter effect remained.

The study, “Harry Potter and the Deathly Donald?,” was written by Professor Diana Mutz, the Samuel A. Stouffer Professor of Political Science and Communication at the Annenberg School for Communication and in the Department of Political Science at the University of Pennsylvania.

In the nineteenth century, Uncle Tom’s Cabin was widely credited with shifting public opinion against slavery, but to date, there has been sparse evidence that fictional stories, even very popular ones, can influence political opinion. Evidence has largely come from laboratory experiments — for example, forcing people to read one of two stories — rather than observing real-world consumption of fictional stories.

Harry Potter’s popularity, with more than 450 million copies sold worldwide, made such a study possible in the public as a whole.

“Because Trump’s political views are widely viewed as opposed to the values espoused in the Harry Potter series,” Mutz writes in the study, “exposure to the Potter series may play an influential role in influencing how Americans respond to Donald Trump.”

To test that explanation for the Harry Potter effect, Mutz focused on three core themes from Harry Potter: The value of tolerance and respect for difference; opposition to violence and punitiveness; and opposition to authoritarianism.

In each case, Mutz points out, Donald Trump’s messages are opposed to the lessons conveyed in Harry Potter and closer to that of his enemy, Lord Voldemort. Examples abound throughout the series:

Harry and his friends advocate for oppressed house-elves and oppose Lord Voldemort’s quest for blood purity among wizards. Harry himself is of mixed wizard/muggle (non-wizard) ancestry. Trump, by contrast, has called for a temporary moratorium on Muslim immigration and made offensive comments about outgroups of all kinds, including women, Mexicans, Asians, and those with disabilities.

The Harry Potter series promotes non-violent means of conflict resolution; while Voldemort is willing to kill many times, the books’ protagonists consistently avoid unnecessary curses for killing, torture, or controlling others. Harry even saves the life of his Voldemort-aligned nemesis, Draco Malfoy. Trump, by contrast, has spoken widely about his fondness for waterboarding, and advocates the killing of terrorists’ families as a means of deterrence. He has praised his followers’ acts of violence against protesters at his rallies.

The Harry Potter protagonists work against authoritarian characters in the books. “As does Voldemort,” Mutz writes, “Trump portrays himself as a strongman who can bend others to his will, be they the Chinese government or terrorists.”

Mutz polled a nationally representative sample of 1,142 Americans in 2014, and again in 2016, asking about their Harry Potter consumption, their attitudes on issues such as waterboarding, the death penalty, the treatment of Muslims and gays, and (in 2016 only) their feelings about Donald Trump on a 0-100 scale.

Party affiliation did not affect the likelihood that a person had read the Harry Potter books, the study found; Democrats, Republicans, and Independents have all read Rowling’s books in roughly equal numbers.

The study found that each Harry Potter book read lowered respondents’ evaluations of Donald Trump by roughly 2-3 points on a 100 point scale.

“This may seem small,” Mutz acknowledges, “but for someone who has read all seven books, the total impact could lower their estimation of Trump by 18 points out of 100. The size of this effect is on par with the impact of party identification on attitudes toward gays and Muslims.”

Mutz’s data also shows that each Harry Potter book read also raised a person’s evaluations of Muslims and homosexuals, two groups chosen to gauge the respondent’s tolerance and respect for difference. Harry Potter also appeared to encourage opposition to punitive policies — gauged by responses to questions about the use of torture, killing terrorists, and support for the death penalty — though the effect size was small.

But reading Harry Potter also engendered opposition to Trump in ways that surpassed the effect of these two themes.

“It may simply be too difficult for Harry Potter readers to ignore the similarities between Trump and the power-hungry Voldemort,” she writes.

Mutz also collected data on viewership of Harry Potter movies, but found that these did not predict Trump opposition. This may be because of pre-existing partisan patterns in movie viewing whereby Republicans were less likely to see the movies than Democrats. Moreover, reading inherently requires much higher levels of attention and allows for greater nuance in characters, many of whom are neither wholly good nor wholly bad. Due to length, movies must leave out material from the full books, and they are more likely to emphasize action over the characters’ internal dilemmas and introspection.

So can Harry Potter defeat Donald Trump?

“Throughout the series, love and kindness consistently triumph over aggression and prejudice,” says Mutz. “It’s a powerful positive theme, and thus not surprising that readers understand the underlying message of this storyline, and are moved by it. These pro-unity views come through loud and clear in the storyline and have also been publicly voiced by the author of the series, J.K. Rowling, who has publicly espoused anti-Brexit and anti-Trump political views. Harry Potter’s popularity worldwide stands to make a difference not just in the U.S. election, but in elections across Europe that involve aggressive and domineering candidates worldwide.”