I have seen at least three fundamentally different analyses of what "happened" with Trump's win on Tuesday night. Each of them has some element of truth to it, but they give rise to very different models for response.
1) The first is well-represented by
this Crooked Timber discussion around Ta-Nehisi-Coates argument that American democracy is fundamentally based on structural racism.
In the context of Trump's campaign and the things he said regarding Latinx and Black Americans (and probably other PoC groups as well, but those were the most prominent), to say nothing of the anti-Semitic undertones of some of the campaign advertising and the makeup of his alt-right supporters, it's obviously an important part of any analysis.
However, if one puts Trumpism and Trump into the broader context of Brexit, of France's Front National and other European nativist parties, it's clear that although race as a marker of in-group/out-group membership is a factor in almost all of these cases, it's hardly the specific historically conditioned form of American racism. In many cases the commonality would seem to be anti-immigrant sentiment (more on that below).
Note the significant support for Trump among Latinx and woman voters: although both explicit and structural racism and sexism are clearly factors in Clinton's defeat (and major factors, especially given the degree to which Hillary Clinton's entire career has been marked by fundamentally sexist evaluations which would have been different had a man been in the same position) this was not simply a revolt by white men against the other.
2) A second, divergent analysis is represented by
Naomi Klein's Guardian article arguing that the fundamental problem is the underclasses who are losing out to globalism and neoliberalism. A milder form of the argument identifies the discontent driving Brexit, Trumpism, etc. with those who have lost work as a result of economic changes in the past two decades or so.
This argument at least takes the requirement of finding a generalizable course seriously. And it also has an obvious element of truth to it: the left is failing to mount much of a systematic alternative to the current system, and there certainly were Trump voters who had supported Sanders in the primaries. To the degree that anger at the elites is driven by income inequality and similar outcomes of the current system, it's certainly one underlying cause.
The problem is that the analyses of the makeup of Trump's vote and the Brexit vote (at least) suggest that the real losers are not driving the rejection of elite politics; instead the key demographics are those who are not at the sharp end of the stick, but rather those somewhat up the social and economic scale. They have certainly seen wage stagnation and the hollowing-out of rural life (they are, as a majority, rural), but they aren't dominated by the unemployed factory workers whose jobs have moved elsewhere. (This is not to say that such workers did not make up part of Trump's support; they were only part of it, however.)
In this context it's worth looking at the solution suggested by this analysis (and pushed quite heavily in Klein's article): that what is needed is a new firmly left-wing populist platform to provide an alternative to right-wing nativism. Developing a new progressive model which goes beyond tinkering at the edges of the system (the approach taken by the Clinton campaign) is a good thing in itself, but I see no evidence that as a way of confronting the current wave of events it would have been, or would be, successful. Corbyn has the firm support of the majority of Labourites, and Labour is not exactly succeeding at capturing the UK. In an election between Sanders and Trump, although there are certainly some ex-Sanders supporters who moved to support Trump, it's hard to believe that they outnumbered the centrists and less conservative Republicans who were willing to vote for Clinton but would have balked at an explicitly socialist candidate. Klein puffs the Leap Manifesto (while skimming over the fact that it's basically a family project) without noting that it's a manifesto for a party which has never come within any reasonable distance of national power (and the closest it came was under a relative centrist, Jack Layton, against a very unpopular Liberal leader as the alternative opposition choice) and which has been decried by the branches of that party that are actually in power provincially.
In the absence of this sort of economic dislocation, the anger fuelling Trump's win would have been less powerful, less widespread, and he would probably have failed. So in that sense it's a "cause"; but it's hard to imagine a progressive agenda to fix it which would have won in the context of the US. (The case of Brexit is special: an intelligent progressive would never have called the referendum in the first place. Ok, you can replace "progressive" with "human" in that last sentence.)
Note that a more aggressively progressive left is less likely to get anywhere if a significant source of malaise if future shock or its equivalent. Which leads us to...
3) A third analysis points at anger at fundamentally cultural change: Brexit voters who are Little Englanders, Americans who are nostalgic for the 1950's, people who really don't want to face anthropogenic climate change and thereby have to change their habits, rural dwellers whose communities are being hollowed out by internal shifts towards the cities as farming becomes more agribusiness and countries as a whole become more urban, Evangelicals who resent increasing secularism and immigrants with other religions (whether different faiths such as Islam or just different variants such as Hispanic Catholicism).
Resentment of immigration may slot into this model better than into point (2). Importing Mexicans to pick crops (à la
George Murphy) does not obviously displace US workers; likewise, the NHS nurse from Poland at a local English hospital has probably been hired in the absence of sufficient English applicants for nursing positions. Both, however, are markers of change.
This fits many aspects of the general situation relatively well.
First, there's basically nothing that can be done about it. It's all very well to declaim "Turn back the universe and give me yesterday", but it won't work. Even a "succesful" imposition of political reaction does not restore the social fabric of the past (the German states of 1825 were not very much like the German states of 1785, regardless of what Prince Metternich was able to do).
I'm willing to bet that one of Trump's promises which will not be fulfilled is the full mass deportation of "unlawful immigrants": too many economic interests would be impacted (fruit is already withering on the vine in some areas because of an insufficient workforce). There may be a few dramatic staged raids of some form or another, but there will be nothing systematic and long-term. (Ditto with the wall: Congress is not about to authorize that expense.)
Secondly, it's always been around, in one form or another. (There have been long periods when social change moved at a snail's pace, but not since at least the Sixteenth Century.) My grandfather, who died in 1978, was born on a farm in the Annapolis valley where horses were the primary source of power and where there was no such thing as plumbing or electricity; by the time he died (living in Toronto) the Apollo missions were over, he drove a car and lived in a multicultural apartment building, and had lived through all the changes of the Twentieth Century.
Thirdly, insofar as some of this sort of malaise is driven by loss of relative status, or the fear thereof, any attempt to address it will result in keeping some variant of "the lower orders" down. (Hence the close relation of this sort of concern with point (1), and its close relation to analyses of privilege.)
If this is the biggest driver of this sort of electoral shift - a permanently angry and emotionally deracinated electorate - then it's not going to go away. (Immediate champions will be up like a rocket and down like the stick, as they prove unable to address the change fuelling the anger.)
The one upside of this is that there is something that can be done, if the analyses are correct: there is a negative correlation between educational level - a proxy for "being better informed" - and support for this sort of politics. Increasing the number of educated members of the population as part of a general initiative shows some promise of blunting this type of political force.
Finally, it's worth noting that none of these factors is "the" explanation for a Trump win: it was fuelled by a combination of general factors as well as by contingent events (it is arguable that Comey's intervention might have cost Clinton the Presidency, and even more arguable that a Clinton identical in all other respects who had not had a private e-mail server would now be President-elect).