Populism, according to Wikipedia,
refers to a range of approaches which emphasise the role of “the people” and often juxtapose this group against “the elite”. There is no single definition of the term, which developed in the 19th century and has been used to mean various things since that time. Few politicians or political groups describe themselves as “populists”, and in political discourse the term is often applied to others pejoratively….
[T]he ideational approach … defines populism as an ideology which presents “the people” as a morally good force against “the elite”, who are perceived as corrupt and self-serving. Populists differ in how “the people” are defined, but it can be based along class, ethnic, or national lines. Populists typically present “the elite” as comprising the political, economic, cultural, and media establishment, all of which are depicted as a homogenous entity and accused of placing the interests of other groups—such as foreign countries or immigrants—above the interests of “the people”. According to this approach, populism is a thin-ideology which is combined with other, more substantial thick ideologies such as nationalism, liberalism, or socialism. Thus, populists can be found at different locations along the left–right political spectrum and there is both left-wing populism and right-wing populism.
Just as “the elite” isn’t homogeneous, neither is “the people”. True populism therefore demands a decentralized polity, according to the principle of subsidiarity:
[M]atters ought to be handled by the smallest, lowest or least centralized competent authority. Political decisions should be taken at a local level if possible, rather than by a central authority.
This is a conservative principle because deciding matters locally means that they are usually handled in accordance with social norms that prevail locally, and which reflect local conditions. This is in contrast with one-size-fits-all “solutions” imposed by distant officials who have no appreciation of local knowledge and norms, and who — in any event — are usually hostile to those things.
Subsidiarity is also, in theory, a libertarian principle. Too many self-styled libertarians, however, are quick to abandon the principle in favor of state-imposed rules that favor their views about how “society” should be organized. Thus — and to the detriment of social comity and stability — we have state-imposed abortion, a state-imposed edict to honor same-sex “marriage”, state-imposed “tolerance” of unsafe sexual acts, the rending of families by lax divorce laws, and on and on.
It is populist resentment of elite dominance that enabled Trump’s electoral victory. “Drain the swamp” is a good part of it. The rest is mainly a desire for the preservation (or restoration) of traditional American culture, the protection of which requires selective immigration and strong defenses.
The principle and spirit of populism — and its enemies — is captured by Bertrand de Jouvenel in his 1945 epic, On Power: The Natural History of its Growth:
Every Power is sure to attack centrifugal tendencies. But the behaviour of democratic Power offers in this respect some peculiar features of a striking kind. It claims its mission to be that of liberating man from the constraints put on him by the old Power, which was the more or less direct descendant of conquest. But that did not stop the Convention from guillotining the Federalists [in the French Revolution], the English Parliament from wiping out, in some of the bloodiest repressions of history, the separatist nationalism in Ireland, or the government at Washington from launching a war such as Europe had never yet seen to crush the attempt of the Southern States to form themselves into a separate unity….
This hostility to the formation of smaller communities is inconsistent with the claim to have inaugurated government of the people by itself, for clearly a government answers more closely to that description in smaller communities than in larger. Only in smaller communities can citizens choose their ruler directly from men whom they know personally. Only in them can justification be found for the encomium pronounced by Montesquieu:
The people is well fitted to choose …. The people knows well whether a man has often seen active service and what successes he has won: therefore it is well equipped to choose a general. It knows whether a judge attends to his duties; whether most people leave his court satisfied; whether or not he is corrupt: therein is knowledge sufficient for it to elect a praetor…. These are all facts which make a public square a better-informed place than the palace of a king.
But the new men whom the popular voice has made masters of the imperium have never shown any inclination to a regime of that kind. It was distasteful to them, as the heirs of the monarchical authority, to fritter away their estate on subordinating themselves. On the contrary, strong in the strength of a new legitimacy, their one aim was to increase it. Against the federalist conception [the Abbe] Sieyès [1748-1836] was their mouthpiece: “… a general administration which, starting from a common centre, will reach uniformly to the remotest parts of the Empire — a body of laws which, through its elements are provided by the body of citizens, takes bodily form at as distant a level as that of the National Assembly, to whom alone it belongs to interpret the general wish, that wish which thereafter falls with all the weight of an irresistible force on those very wills which have joined in the formation of it.” [Liberty Press edition (1993), pp. 286-288, links added, emphasis in original]