Donald Trump isn’t a fascist; he’s a demagogue. That's why he's so dangerous.

The media’s favorite guessing game is to figure out what Donald Trump really believes. Over the past several days, he has repeated his vitriolic remarks about immigrants, promised once again to kill the families of terrorists, declined to dissociate himself from the Ku Klux Klan, and retweeted a quote by Benito Mussolini. Taken together, many commentators have argued, this suggests that Trump is nothing less than a fascist.

But there is also evidence to the contrary. After all, Trump has also praised the state-run health care system in Canada and come to the defense of Planned Parenthood. At the last Republican debate, he repeatedly attacked his main rivals from the left — suggesting that the state has an obligation not to let the sick die on the side of the road, and that the immigrants he would deport should have a chance to come back to the United States. Deep down, other commentators have therefore responded, Trump is actually a moderate.

This whole debate, as Max Weber realized nearly a century ago, misses the point. That’s because, unlike both run-of-the-mill moderates and dyed-in-the-wool fascists, Trump is not motivated by deep political values — and even less so by specific policy preferences.

But this ideological flexibility, Weber explained in "Politics as Vocation," his magisterial 1919 lecture on the nature of politics, does not make politicians like Donald Trump less dangerous; on the contrary, it turns them into a profound threat to the survival of democratic politics:

Vanity, the need personally to stand in the foreground as clearly as possible, strongly tempts the politician.... This is more truly the case as the demagogue is compelled to count upon "effect." He therefore is constantly in danger of becoming an actor as well as taking lightly the responsibility for the outcome of his actions and of being concerned merely with the "impression" he makes. His lack of objectivity tempts him to strive for the glamorous semblance of power rather than for actual power. His irresponsibility, however, suggests that he enjoy power merely for power's sake without a substantive purpose. Although, or rather just because, power is the unavoidable means, and striving for power is one of the driving forces of all politics, there is no more harmful distortion of political force than the parvenu-like braggart with power, and vain self-reflection in the feeling of power

Weber knew that the problem of demagogues is as old as democracy itself, and that in their recklessness they can provoke great upheaval or even civil war. True believers may be willing to sacrifice anything for their cause. But they have goals that can be obtained and values that guide how (not) to act.

Demagogues, by contrast, are willing to do or say anything to gain office or to consolidate their power. Unconstrained by ideology, they have no concern for the consequences of their actions. Anything that serves to make them more powerful is good enough for them — even if the political system that facilitated their rise should be destroyed in the process.

This, rather than some deep similarity to fascism, also explains the affinity between demagogues and political violence. True fascists venerate violence but also want to make it serve a purpose larger than themselves, like territorial conquest. Demagogues, on the other hand, tap into the most violent currents in a population simply to bolster their own popularity.

In the process, they often unleash lethal damage: They wreck the informal rules of civility that democracies require to survive. Once voters are activated along violent lines and fervently believe the myths propagated by the demagogue, the dam is broken; the ordinary rules of democratic politics no longer apply, and there is no telling what might come next.

Daniel Ziblatt is a professor of government at Harvard University and the author of Structuring the State: The Formation of Italy and Germany and the Puzzle of Federalism.

This post is part of Polyarchy, an independent blog produced by the political reform program at New America, a Washington think tank devoted to developing new ideas and new voices. See more Polyarchy posts here.