Despite these caveats, the general trends are poor for Republicans. In almost all of our scenarios, Democrats improve their performance in the popular vote and electoral college as their groups grow as a share of the electorate and Republican groups shrink.

What about the two dueling GOP strategies of expanding support among immigrant groups or further increasing support among non-college whites? Clearly, Republicans would benefit from increased backing from either group. A 7.5-point boost in support among immigrants would lead to GOP victories in 2020, 2024 and 2028, although Democrats would win starting in 2032. Alternatively, a 5-point increase in GOP support among non-college whites would lead to Republican electoral college victories at least through 2036.

To the extent that there is a trade-off between these strategies, increased support for Republicans among non-college voters is generally more significant because while it will shrink over time, it still represents a very large percentage of eligible voters: 47 percent in 2016.