Last week, two men in Boston allegedly beat a Hispanic homeless man. Afterward, one of the two brothers told the police, “Donald Trump was right, all of these illegals need to be deported.”  Trump’s response?  “I think that would be a shame,” he said, adding, “I will say, the people that are following me are very passionate. They love this country. They want this country to be great again. But they are very passionate. I will say that."

And that showed what Trump is really about.  His politics depend on the strategic manipulation of what America’s Founding Fathers called “the passions”— emotions that, when stoked, cause us to literally lose our minds. And that’s perilous not only for the fragile state of U.S. politics today, but for Trump’s political legacy.

Trump has described Mexican immigrants as rapists, called Martin O’Malley a “little, weak, pathetic baby,” and said that Fox anchor Megyn Kelly must have had “blood coming out of her wherever” when she questioned him during the first GOP debate.

His statements are completely consistent with his approach to both his business and entertainment careers, which was to connect with people’s guts at the expense of their reason. In his 1987 book, The Art of the Deal, Trump explained his modus operandi: “The final key to the way I promote is bravado. I play to people’s fantasies.  People may not always think big themselves, but they can still get very excited by those who do.  That’s why a little hyperbole never hurts.  People want to believe that something is the biggest and the greatest and the most spectacular.”

There has been a tremendous amount of discussion about the “anger”and “frustration”of Trump’s supporters. But it’s not just anger. Tapping all of the passions, including avarice and lust, is the unifying theme of his career. And therein lies the problem.

People have been wrestling with the problem of the passions in politics as far back as Plato and Aristotle. Plato described three parts of the soul—the appetites (like lust), the spirited (military courage), and reason. Reason was a charioteer trying to control the “dark steed” of the passions. The only way to control the appetites was to force the horse to the ground and whip him until he bled.

It’s a violent metaphor, but the ancient diagram has proven stable, continuing today in modern brain science, and even the Pixar movie Inside Out, which tracks the teenage protagonist’s struggle to understand and control her inner impulses.

The problem of the passions in politics was central to the thinking of America’s founders, as well. Take James Madison, the father of the Constitution. As a boy studying with his tutor Donald Robertson, Madison first learned the idea that “our passions are like Torrents which may be diverted, but not obstructed.”

In college, Madison was taught by the great Scottish cleric John Witherspoon that passions originated in an object of intense desire. Passions of love included admiration, desire, and delight. Passions of hatred were envy, malice, rage, and revenge. Most important however was the “great and real” distinction between selfish and benevolent passions. A benevolent passion, Witherspoon taught, came from the happiness of others. A selfish passion stemmed from gratification (like Donald Trump’s stroking of his own ego)—and was the most dangerous to a republic.

The passions are slippery for anyone seeking to control them, particularly in democracies with free speech. But that doesn’t mean they can’t be tamed.

America’s Founders sought to govern the passions. In Federalist No. 10, Madison recognized the danger of faction, which would “kindle ... unfriendly passions.”  That required, in turn, checks and balances and institutions like the Senate to “refine and enlarge the public views.” One reason the framers designed the Electoral College, in fact, was so that the electors could put a stop to a candidate who rose to power by playing to the people’s prejudices at the expense of deliberation and education.  Over the decades, these ideas became deeply entrenched in American political culture, leading Alexis de Tocqueville to praise American mores—“habits of heart”—that undergird self-governing citizenship. This constitutionalism helped American democracy thrive, and serves to check demagogues.

An optimistic read would be that those cultural factors are contributing to Trump’s apparent ceiling in the polls. Although he has found a base of Republicans who relish the out-of-control, others oppose him, many for that reason.

So what’s the real danger of the passions in politics today? After all, the U.S. has plenty of checks and balances, and a far more inclusive democracy than at its founding.

Think, for a moment, of former Italian Prime Minister Silvio Berlusconi—at least at first glance, a startlingly similar figure to Donald Trump. Berlusconi became the country’s richest man by creating Italian television shows that flaunted near-naked bodies, and stories of lust and betrayal.

Even as prime minister, Berlusconi was rather transparently prisoner to these same passions, holding “bunga bunga” parties, and otherwise launching a debauched festival of greed, through a political culture of bribery, corruption, and tax fraud.

The danger with Trump would seem to be that, like Berlusconi, he would be hoist by his own petard, self-destructing precisely through the agent of his rise, and dragging the rest of us with him.

But consider an alternative hypothesis: Trump himself isn’t a creature of the passions; he’s instead strategically employing them as a means to his own ends.

Take greed. He’s been cited many times for what now has become a chestnut: “The point is, you can’t be too greedy.” He’s also come to be known for his braggadocio about his net worth during his 2016 run. But his approach to money is usually much more nuanced and self aware. In The Art of the Deal, he writes, “Money was never a big motivation for me, except as a way to keep score. The real excitement is playing the game.”

The same could be said of virtually every other element of the Trump show: Trump is playing his base through the passions. That’s why, on every supposed “gaffe,” he just doubles down, befuddling the pundit class, but tapping into his “very passionate” base.

The real danger is not that he will become Berlusconi-esque. It’s that he will further erode the political institutions necessary to getting things done. Every great challenge facing the country will require complex negotiations between different parties with a faith in the process and subject matter knowledge. And every unruly passion he stokes, from lust to outright fury, is another small explosion under America’s already-rickety policymaking foundation.

He might also consider episodes from the last century that show a politics of the passions getting the better of the politician.

In 1950, for instance, Wisconsin Senator Joseph McCarthy opportunistically chose to stoke the public’s anger at Communists by using his House subcommittee in a crusade later famously characterized, by Arthur Miller in The Crucible, as a witch hunt. McCarthy’s reign was dangerous, but it lasted only three years, and it was attorney Joseph Welch’s heartfelt cri de Coeur during the Army-McCarthy hearings in 1954—“Have you no sense of decency, sir?”—that rang the loudest. His fall was even swifter than his rise.

While Trump revels in support, he could do a lot of damage. If Trump wants to be successful within the context of American history and its political culture, he should start by replacing the exploitation of the passions with a layer of statesmanship. That would not only help our politics, it would be in his own best interest. For in the end, Americans can be quite unforgiving to the politicians who prey on their prejudices.