Oh look, this debate again.
https://www.merriam-webster.com/words-at-play/patriotism-vs-nationalism
https://www.quora.com/What-is-the-difference-if-any-between-nationalism-and-patriotism
Patriotism and nationalism are not interchangeable, haven't been for a while, but long ago were
Trump is not the fool he wants others to think he is. This statement by him, specifically, is how he panders to white supremacists.
I suppose it's a matter of generation and what you are used to, and I absolutely hate to agree with him about anything, but the definition 'slow' gave is the one I grew up with. Nationalism was what the subject peoples of the British, and other European Empires, had as they tried to achieve self-determination. Hence Irish Nationalism, The Indian _National_ Congress, Arab nationalism, etc. We still have the Scottish Nationalists. Patriotism, on the other hand, was the slightly smug and chauvinist attitude of established imperial powers convinced their country was the best. Thus nationalism good, patriotism bad.
That Mirriam-Webster explanation is very interesting, especially the bit about nationalism being a political movement. I think that's a crucial characteristic whether it takes a 'progressive' or reactionary form.
I actually wonder if it's something to do with the difference between a nation and a country. A nation consists of a people, (you don't even need a country, e.g. Nation of Islam) allegiance to a nation means prioritising your membership of that group of people, and so carries an intrinsically populist element (which, crucially, could be left or right), whereas patriotism, love of 'country' is more about an institutional allegiance, and is a feature of people who feel they already securely _have_ a country not just a people, and a belief that the particular institutions of your country are superior.
A patriot loves what they see as the values and institutions that they see (almost certainly wrongly) as uniquely a feature of their country, a nationalist probably mostly loves something they consider a defining characteristic of their people (which in the case of US and Europe is very likely to include whiteness)
To embrace nationalism while being a citizen of a country that is already independent and under no existential threat suggests power combined with fear, a power that doesn't realise it's a power, a group who _think_ they are victims when they aren't, really. Which seems exactly right for Trumpism.