Nationalism is dead but a lot of people still believe in it. Something you might have missed is that a lot of Brits voted for UKIP because it promised to invest more money in Britain’s National Health System. Meanwhile, Trump could only attract the attention of working-class Americans with vague promises to increase Social Security (basic income for Senior Citizens) payments and implement single-payer healthcare. Thus nationalists can only attract voters attention with promises of benefit increases.
Hence nationalist politicians like Trump and Nigel Farage know nationalism is dead. Unfortunately, a lot of progressives have not received the memo.