@Thomas,
On the macro sense I think that nationalism in general is in decline with globalization and greater economic contagion. I think enmity with immigrants is something that has always ebbed and flowed but that nationalism in general and isolationism is generally a desire to move backwards or hold in place versus the advancement of globalization and multiculturalism.
To me the term (while like all political labels being imperfect) has pretty clear and useful meaning:
people who in general prefer change as a way to improve society vs people who generally prefer to prevent many changes or to go back to the way they were to improve society. On the small scale almost anything can be portrayed as a change but on the larger scale the politics tends (though there will always be exceptions) to align with these general tendencies in a general conflict between previous values and future values.
If seen that way progressive politics correlates well with American liberal politics in my opinion and from a linguistic perspective is not seen as very different, it's just a better antonym for conservative than "liberal" ever was and is gradually replacing that term for that reason (makes more inherent sense as a political label than does "liberal").