The Country Has Shifted Right Because Liberals Did Not Have Enough Kids to Keep Up Their Share of the Population

This is not the only reason, but it is the foundation of the others.

Demography is not everything, but it is the single most powerful fact about a society.

Conservatives have more kids than liberals. 

Discomfort in the Search for Truth

If, in your search for truth, you never run across a fact that is uncomfortable to your ideology, you are doing it wrong.