The system is designed with the assumption that politically elected representatives would seek compromises in an attempt to reach what is best for the country, making sure it is very difficult for one fraction to get absolute political power.

The Republicans at some point realized the dominant strategy in this system, assuming their goal is power rather than the improvement of society, is to never compromise and to fuck everyone over at every option. The way the system is designed they are in a great position to do a lot of damage that way.