The American Left generally welcomes immigration, but opposes foreign trade. There are exceptions of course, but generally the further left one moves this combination of policy preferences is even starker. Bernie Sanders seems wholly opposed to free trade and yet favors immigration. Indeed, he wants to make citizens of immigrants, even if they have come here illegally.
What explains this divergence? It cannot plausibly be concern for low-wage workers in the United States. It is true that trade, while being generally beneficial, can depress the income of low-wage workers (at least in the short term), because they must compete more with low-skilled workers elsewhere. But the effect of low-skilled immigrants is the same. It puts pressure on the wages of low-skilled Americans.
It can’t be concern for the poor abroad.