The issue is that the senate can be filibustered with 5% of the US population's backing. A majority vote requires 8%. A fillibuster-proof majority requires 12%.
This implies that it would not take many geographically mobile liberals to end the Republican party forever.
Ironically, the Republican party invented this technique back when they were what we would currently call a liberal party. It worked great. Read up on carpetbaggers.