Though I agree that the tweet was ripe for criticism, I didn't see the this as having the same connotation as have similar statements from other times in our history. I think the classic reference is that which was made by some to the African-American community who'd expressed dissatisfaction with how they were treated after being freed from slavery. If I read this correctly, the other part of Trump's comment referenced these person's place of heritage and the difficulties folks faced in those countries. I read his comment as something like 'If you're not happy here, go back and fix these things in the country of your heritage and bring that fix back here'. I didn't read anything related to permanence. However, you should know by now how our media spins things anyway they wish.
I also don't see what this has to do with racism unless, if the same comment was made to a person of German or French descent, it was also considered as racist. The knowledge that the four persons were not "anglo" does not, IMO, in and of itself make this a racist comment. However, shouting "racism" has become a popular way to avoid further conversation. It's the new "nuclear option" adopted by many. Just my opinion but I'm just an old gray haired white guy descended from a mix of European cultures...the new scourge in America.