Populism divides society into two antagonistic camps, a virtuous and homogeneous people against a corrupt and self-serving elite, and holds that politics should express the general will of the first against the second. Whether it amounts to an ideology at all is disputed. Cas Mudde's influential account calls it a thin-centered ideology that attaches itself to fuller ones, which is why it appears on both left and right without contradiction.
The American People's Party of the 1890s gave the word its name, mobilizing indebted farmers against banks, railroads and the gold standard and finding a voice in William Jennings Bryan's Cross of Gold speech. Latin America produced the most durable variant in Perón's fusion of labor mobilization, nationalism and personal authority. Postwar European populism has been predominantly of the right, defining the people ethnically and against immigration, while Podemos and Syriza represented a left populism theorized explicitly by Ernesto Laclau, who took the construction of a popular subject to be the essence of politics and not a pathology of it.
The most consequential dispute is whether populism is anti-democratic. Jan-Werner Müller argues that its defining feature is anti-pluralism, not anti-elitism: the claim to be the sole legitimate representative of a people whose true will cannot be divided, which makes opposition inherently illegitimate and turns electoral defeat into evidence of fraud. Others hold that populist surges are a corrective, symptoms of genuine representative failure, and that treating them as pathology is itself the elite reflex being complained about.
The recurring difficulty is that the people it invokes has to be bounded by someone, and the boundary is rarely drawn by the people themselves. Its defenders point out that every democratic theory has this problem and that populism at least states it openly.