Make your party about the economy. I know that will be tough as your party is responsible for much of the recessions and has a record of tanking the economy when you have the white house, but it is the one issue which still gets traction.

Loose the religious nuts.
Loose the hyper patriots.
Loose the racists.
Loose any subgroup on the far right.

As was the case before your side went nuts, you stayed to the right of center, but just. Those voters to your right vote with you as they vote against the center and the left.

Take Ike, and Nixon for example. More center and common sense then fringe. Hell, Ike prosecuted the Birchers.

Otherwise, feel free to keep on Wigging out. America has done just fine with a marginalized KKK.