My dad fought the Nazi's they lost. The world knows it. What is the deal with their recent resurgence?

Because a specific group of populists 'lost', but populism still works and will continue to work wherever there is people in dire situations.

The more dire your situation is, the more you need a solution. And then someone telling you "it's the fault of those other people", that just offers up a real straightforward supposed solution.

Even if it's pretty clear that it cannot possibly actually solve the real problem, the prospect of a mild improvement will have many going along and ignoring morals.