Whether it is the Supreme Court, or tax sanity, Republicans win policy fights because they are always consistent, while democrats are always muddled and muddy in terms of strategy and desired outcomes. It has nothing to do with the merit of the contending arguments.
Take an issue such as gun sanity. Republicans messaging is always in line with the most conservative possible messaging. Let’s put that coherent and consistent conservative massaging on a scale and call it C5 (most conservative).
Imagine the range of possible positions on any given issue running from C5 most conservative to L5 (most liberal). Eg. “C5 – C4 – C3 – C2 – CL1 – L2 – L3 – L4 – L5”
On an issue such as such as gun sanity, for example, you will have Democrats and liberals taking every possible position from L5 to C4. This random hodgepodge of positions and opinions gives Republicans a huge advantage when every Republicans promotes the C5 positions over every media at all times.
It is a built in advantage that Democrats will never overcome. 
