When I wrote my 2013 series on demographic shifts, including the Case of the Missing White Voters, I outlined a potential path to electoral victory for Republicans that didn’t involve reaching out to non-white Americans as such. Rather, I suggested that a more economically populist Republican Party that was more skeptical of American intervention abroad, aligned against illegal immigration and skeptical of trade deals — and that, above all else, didn’t nominate a guy with car elevators as its standard-bearer — might be able to gain the enthusiastic backing of enough blue-collar whites to win elections. This incarnation of the GOP might eventually win over some non-white voters, who vote for Democrats more because of their stances on economic issues than their stances on identity issues.
This is more-or-less the path that Trump took. Indeed, he proved a stronger version of the “Missing Whites” approach than I had thought was possible, by alienating large numbers of whites with college degrees, who had previously been the foundation of the Republican Party.
But there are limits to what can be done with whites without college degrees, who constitute a significant portion of the electorate, but not a majority. While Trump has, in fact, made progress with non-whites, his bleeding of support among whites with college degrees, especially women, and (at least according to polls) older white voters more than offsets that.
In other words, at a certain point you just run out of groups that you can afford to alienate from your coalition, and Trump may well have hit that point.