About the rise of nationalism… many speculate about the reasons for that. That was by the way happening before Trump already, I feel Trump is more like part of the phenomenon, not a special case.
I personally think this has to do with economical differences created in part by globalization. In the last decades in the western world (europe, north america) the differences between rich and poor get bigger and bigger. This is a result of policies installed by Reagan and Thatcher and then followed by Bill Clinton and Tony Blair. We had similar things happen in many countries, in germany for instance Helmut Kohl (conservative) was followed by social democrat Gerhard Schröder.
All of them realized economic reforms, that in the end helped the economy along the globalization, but at the cost that social securities were cut and some people fell through the cracks. At the start this were only a few, but over time more and more people felt lost economical, seeing the country flourishing and rich people get more rich, while these people had a hard time to come by. You can see it at the rise of people, that are unable to stem unexpected expenses, like if your car breaks suddenly down you don't have enough to repair it. And this development was slowly, at first only a few people were lost along the lines.
Politics mostly ignored them, at first this was without repercussion as these were too few. For a long time then no one cared about them. Until nationalists realized their chance and blamed everything on migrants and globalization (although globalization itself would be fine as long economic policies would provide social security adapted to globalization). This is in my opinion the reason, nationalists targeting the poor and classic politicians ignoring them. This includes the left, which in the past was for the poor man, but mostly ignored the struggles in the past and focused more on identity politics and climate change. Without a doubt important topics, but they ignored the poor people.This feeling of being ignored by classic politics led more and more to anger, which is utilized by the nationalists.
EDIT: By the way, your sig shows this. Back then movies like They live showed the struggles of poor people. Remember the main characters being poor (and moreso a white and a black guy working together both being poor and both being in the same situation) and all the obey, consume stuff is symbolic for the situation. This movie wasn't alone, many movies back then showed poor people, also tv shows, remember Roseanne. But Hollywood elites stopped caring about poor people, this leading to todays movies practically never use poor people as heroes or even displaying the struggles of poor people. This is all part of the feeling of many, that all the "above", be it in politics or media, ignore the poor. This feeling of being outside is what helped the nationalists taking over.
It certainly makes sense. But it doesn't explain the issue entirely, I believe. Otherwise a lot of people in East Germany, for instance, would not have traded Die Linke for the AFD. Like Rol mentioned, the vote for the nationalists etc. strongly correlates with the countries where xenophobic sentiment is stronger - Italy, Poland, Hungary.
We'll see how these countries will vote when faced with a recession under these governments, and realize their claims and promises are mostly bull. Italy's probably going to be the first.