Several observations:

1.  His lumping the liberal side with the conservative side and accusing them of the same malady means he is scared for his own side.  Which a more honest person would actually come out and give some constructive criticism of his side hoping to turn the tide before it becomes a flood.  But that is not usually the case with the left (nor the right generally, although they are more prone to self examination than the left).

2. The "independents" or the center are not heading to a third party and are not usually heard because they are the silent majority.  They sit quietly usually just doing their jobs and living their lives and vote every 2-4 years.  It is not the shrillness of the left or right that silences them, but their own disinterest.  Occasionally someone will attach some greater significance to their silence ("they do not like the shrillness" or they want "bipartisanship", or some other such malarkey), but for the most part the "reporters" are trying to project their own feelings on the center.  The center just does not care.

3. Building a new "coalition" has been the goal for all powers since they realized they could not rely on their own side to elect them.  Clinton did an excellent job of it after being smacked down in 94.  Bush started out trying that with his "compassionate conservatism".  Both have been flung on the ash heap of history.  The reason it only works for a short term is the middle is not interested in forming alliances.  They just do not have enough motivation to do so.  Any "coalition" that appears to form is not a unification of ideas with a side, but a rejection of the other side.  Which of course changes when the side they appear to be on, moves again to their base thinking they have established a new majority.