Dwaring on the work of Roger Eatwell and Mathew Goodwin and their book national populism as well and Inglehart and norris you could argue that while populism i.e brexit, trump, was a backlash against both economic and cultural forces that it was primarily a cultural backlash against immigration that populists saw as undemocratic. As cass mudde states ‘populists aren’t principally concerned with economics. instead their focus is cultural’. You could also draw on Eric Kaufmanns book whiteshift and any other sources you think are relevent. The thesis could be something along the lines of populism being a response to the crisis of democrcay rather than causing it. AS John b Judis says populist are often categorized as being antidemorratic but they operate very much within the context of democracy