The difference between the two hinges on economic issues, not social ones.
1. The widening inequality gap between rich and poor.
2. Monopolistic corporations and laissez-faire capitalism
3. Conflict between workers and capitalists.
Liberalism, as defined by Locke in the 1700's originally referred to free market, laissez-faire capitalism and limited government.
My take: Tea Party/Trump has destroyed their position on the right, and so moderate R's are retiring or becoming D's as the Overton window shifts.
I realize I'm generalizing here and no offense is intended to anyone who isn't a a racist or reactionary.