This theory falls short for three reasons:
Demographic change is not evenly dispersed in states and voting districts throughout the country.
Voting behavior is not static. Voters more readily change which party they support than the demography-is-destiny models anticipated.
Despite the large change in the demographic composition of the electorate, most voters still do not self-identify as liberals. In fact, liberals remain bronze medalists in the ideological breakdown of the electorate—ever since the question was first asked decades ago.