Many people ponder why we have political gridlock in Washington DC and in the states.  There are several theories on this, and some of these make make a lot of sense.  More on other theories later.

But one of the important ones that I want to discuss here is what I hear quietly in private, but that these folks will not say in public.  

Politicians who would otherwise be "moderates," especially in the Republican party (but sometimes Democrats too) have been afraid for at least 2-3 political cycles now about a primary opponent from the extreme side of their party -- that is, for example, the right wing of the Republican party.  Thus, they do not fear a general election opponent (especially in districts that are very gerrymandered) as much as they fear a right wing opponent who defeats them in the primary. 

This has been the case especially since 2010 when members of Congress who were measured to be quite far on the right of the party -- such as Robert Bennett of Utah and others -- faced primary opponents (often so-called "tea party" candidates) and were defeated in the primaries.  Bennett, for example was measured as one of the most conservative members of the Senate, but yet was defeated.  Even Senator Hatch faced a spirited primary, as did Senator Grassley.  

When members of Congress see this, and also members of state Legislatures, their reaction is to move strongly to the right.  Even those who have an inclination to be more moderate, and to work across partisan lines, will not do so.  Issues that might work well in a general election (e.g., expansion of Medicaid, tax increases) are likely to lead to primary defeat for Republicans.

Couldn't this same argument work on the left?   Yes, it could, but it is obvious that progressives have been much more forgiving of President Obama's moderation on many issues (e.g., national security, extension of the Bush tax cuts).  And the problem facing the Republican party now is the same problem that faced the Democrats in the post-Watergate era, and led to several years of defeats that taught Democrats lessons.