Populism has a long history in the US, but the term is ambiguous as it's commonly used, and is often given a negative connotation. I use it in the sense that a Populists' support comes from the demos, the public, as opposed to from what we think of as the establishment, and has value for that reason.
Donald Trump's appeals to the racism and nativism of the common man get everyone upset, but he's not causing racism and nativism, only taking advantage of it. He may be making them worse to some degree, which is bad, but is also making people aware that they exist, which is good. People ignore that second part, perhaps because they don't want to own up to its implications. Nor are they acknowledging the good of the fact that the people are having their concerns aired, no matter what they are.
People sometimes say, 'Yes but Mussolini made the trains run on time.' In other words, there was some good to Italian fascism. That's the height of irony, but the trains did run on time.
People use the same logic to justify US Imperialism. It's not that explicit, and much of it is "internalized" and spoken more by how we live our lives.
We Americans have a higher standard of living than people in many places, but we have it in good measure at their expense, the expense of their cheap or stolen resources and cheap or stolen labor, and the expense of their lives sometimes.
Probably two million people have died across the Middle East in the past decade or so as a consequence of US involvement in that region. We don't say, 'Yes, but the trains that take commuters into New York City run on time,' but we might as well. We say the same thing by how we are so oblivious to those two million peoples' lives, by how we shrug off all the negative fallout of US Capitalist Imperialism in general.
Trump, and Bernie Sanders, both in their way are countering that shrug. They are a jolt to the system that embeds it in us. That's good. There's fallout, to be sure, but along with everything else Trump is saying, he's said we should talk to Putin and to North Korea and downsize US Imperialism. That's huge, and it's the opposite of Hillary Clinton, who participates directly in demonizing foreign leaders and killing foreigners.
Foreign policy isn't a focus of the media frenzy around Trump but it's central to how I see things because those two million lives mattered to me. If a few million Americans are upset by Trump, or inconvenienced because the US economy tanks, but two million people who live somewhere else but talk funny and have weird religions are alive, that's good.
I don't share the belief of many that Trump can cause harm to the country. There are many checks and balances in place to prevent this, both formal and informal. Formally
there's the two houses and the courts. Informally there's the huge and
vast government bureaucracy, the media, and last but not least public
opinion. Public opinion served as a check on the most odious social engineering designs of Ronald Reagan and George W Bush. It doesn't stop US warmongering, which is a more significant problem, but that's the issue with Trump.
Trump is reviled by many because he injures their sense of self, which is tied up with nationalism or what we like to cal patriotism, and which, because it is, makes it easier for politicians to pursue foreign wars than to privatize Social Security, which would be less harmful on a global scale than any one of the several wars the US has launched in the past decade.