Dems have to appear to be pro-immigration for reasons (honestly I don't know why this is like this, historically). They are genuinely less xenophobic than the Reps, so they respect the rights of recent immigrants much better. But when it comes to preventing more poor workers coming in, they are just as tough as the Reps. And I believe that's because ultimately they are slightly less captured by capital and therefore more amenable to balance the economy in favor of workers.
Reps on the other hand have to appear xenophobic once again for reasons that aren't super clear to me, but when it comes to actually preventing immigration, they always manage to torpedo their own proposals. And arguably that's because if they passed effective anti-immigration laws, that would negatively affect the interests of capital, the very obvious reason they're in politics for (and Trump is certainly no different).
Maybe now we can resolve this apparent paradox and simply accept that the Democrats are first and foremost the party of the educated, metropolitan and utterly disinterested in matters of material conditions. Whereas the Republicans are the party of people who are bitter towards the first group. Which leads to the conclusion that exceptionally few people in the US are voting according to their own economic interests.