This is a good working definition although Mueller, in the rest of the piece, as evidenced by even his footnotes in the section above seems to be arguing from a conclusion instead of to a conclusion (HT Viva Frei). The conclusion he arguing from is that populism is, described by him in Jungian terms, the shadow side of democracies. Actually the trajectory of the argument would lead him to exactly the opposite conclusion. Populism is, in fact, the very genesis and beginning of democracy. Afterall, the rise of the nation-state in Europe was the dawn of the Enlightenment period. Accompanying the Enlightenment was the rise of democratic political institutions. But, it was the force of populism that broke down monarchies, inherited aristocracies, and even eventually displaced Christendom as the operative political paradigm for Western Europe.
I see liberal capitalism and the rise of neo-feudalism and all manner of elitism in banking, media, the military industrial complex and big tech as the shadow side of democracy and not the other way around! Consolidation and centralization of power is the opposite of democracy and popular rule. The movement to de-centralize and diffuse economic and political power has been part and parcel of the populist enterprise since the dawn of Western democracy.
As far as his criticism that populism engenders xenophobia and the tyranny of the majority, such problems were anticipated by Locke which is specifically why he placed strict limitations on the force of government power, ensuring that civil liberties were protected. Shortly after Locke's writings, the UK passed the Bill of Rights in 1689 and Locke's ideas clearly inspired the US Bill of Rights in 1789, Granted, social inequities and racial discrimination existed. Colonialism and slavery were both still practiced. But even in these instances, it was largely populist movements that encouraged abolitionist movements as well as eventually universal suffrage.
In the modern era, government and centralized power has been interpreted as an impediment to human flourishing. Anticipating contemporary theorizing on the force of governmentality, also referred to in the literature as bio-politics, the French anarchist Proudhon wrote that to be governed means to be “noted, registered, enrolled, taxed, stamped, measured, numbered, assessed, licensed, authorized, admonished, forbidden, reformed, corrected, punished .... repressed, fined, despised, harassed, tracked, abused, clubbed, disarmed, choked, imprisoned, judged, condemned, shot, deported, sacrificed, sold, betrayed ... mocked, ridiculed, outraged, dishonoured”. HT Ferretti in Beyond Electoralism: Reflections on anarchy, populism, and the crisis of electoral politics
The political problem that exists is in our world is the problem of governmentally - how we are to be governed. This was precisely the issue Foucault was grappling with before his death and it remains the key problem today. Framing the problem as populism obscures the entire problem - namely how will we be governed? That means asking critical questions of who governs us how are we being governed? The answer to that question, for me, leads to an analytics of what is called "Neo-feudalism". Populism is one tool to deconstruct the feudal edifice - both historically and presently.
There can be no central program or party of populism since, by definition, populism is diverse. Diverse forms emerge in response to unique circumstances facing a particular community. These communities simply require spaces to organize and develop in order to ensure that the constituents can flourish. Growth is bottom up and not top down. But we have learned in our human evolution that discrimination and colonialism are each negative movements - human rights instruments protects the former and populism guards against the latter (colonialism of all types and descriptions).
By ensuring that we have robust international human rights protections, the tyranny of the majority can be avoided through the development of republican forms of convivial democratic communities akin to what the US founders envisioned (although what they envisioned does not even closely resemble the lived experience of most Americans today). The shadow side of the rise of populist democracy is precisely what is broadly referred to and Neo-feudalism and not the other way around.