3. Immigrants don’t necessarily stay loyal to the party of immigrants.

The Democrats found this out the hard way in the 1980s, as “white ethnics” who had been one of their most reliable bases mass-defected to Ronald Reagan. What happened? For one thing, the immigrants assimilated. “White ethnics” stopped identifying as immigrants, and started identifying as threatened natives. Democrats picked up a lot of votes from new migrants like Hispanics, but the party bled more than it gained. Democrats can’t count on ruling a majority-minority America. Some of those coalition members will probably defect.

4. Whatever Trump does on immigration is probably going to hurt Democrats.

The more people assimilate, the less likely they are to see their ethnic identity as the most important determinant of their political commitments. And the smaller the number of new immigrants coming over to refresh connections to the old country, the faster that ethnic identity dissipates. Let us assume two things happen: Trump manages to eke out eight years in office, and he actually takes strong steps to stem the tide of immigration. What would the emerging Democratic majority look like then? Probably not so hot. Just as Obamacare created new facts on the ground that are making it hard for Republicans to simply return to the old status quo, whatever Trump does on immigration will not only make it harder for Democrats to build the envisioned majority-minority coalition, but also make it harder for them to simply get back to a place where they can wait for it to dawn.