I know a lot of Republicans who used to be Democrats.
Question: Why did they leave the Party of their mothers and fathers?
Answer: Abortion, busing, political correctness, same sex marriage, affirmative action, etc..
As long as the Democrats want to chase pro-lifers and cultural traditionalists out of the Democrat Party, they will continue to lose at the state level and at the federal level.  
Currently: The GOP controls the vast majority of governorships, state legislatures, US Congress, US Senate, state and federal judgeships, and members of the SCOTUS.  
The GOP took over when it embraced culturally traditional policies (this was Nixon's idea), and the Democrats either ignored them or totally rejected them.
Prior to 1965, both parties were culturally traditional, with a few exceptions.
Ted Kennedy was pro-life; that was the Democrat Party back then.
Today, if you are a traditionalist or even a moderate/centrist on cultural issues, then you have only one home: The GOP.