Sometime in April 2014, somewhere in a hospital in California, a Latino child tipped the demographic scales as Latinos displaced non-Hispanic whites as the largest racial/ethnic group in the state. So, one-hundred-sixty-six years after the Treaty of Guadalupe Hidalgo brought the Mexican province of Alta California into the United States, Latinos once again became the largest population in the state. Surprised? Texas will make the same transition sometime before 2020.

When that happens, America's two most populous states, carrying the largest number of Electoral College votes, will be...