Might we be headed toward another four-party moment? There are two reasons to say “yes.” 

Causing this breakdown, in Piereson’s view, are the mounting inefficiency and cost of government, which fuel conservative demands for radical shrinkage of the state, coupled with the decreasing productivity and perceived unfairness of the economic system, which fuel a liberal demand for radical expansion of the state.

The second reason is the course of the current campaign, which has been more about the internal struggles of Republicans and Democrats than the differences between the two parties. 

The usual methods of co-optation by which Republican and Democratic politicians have maintained cohesion within their respective big tents are proving remarkably ineffective. 

The likely scenario for 2016 is that Republicans and Democrats will hang together, though the specific ideological agenda that emerges from their respective primaries is still very much up for grabs. The incentives to avoid actual party crackup are overwhelming; and the resources at the disposal of establishment Republicans and Democrats remain formidable.