comment: >
  
  There have been a few party systems in the United States over the course of its existence.
  Usually, it plays out like this:
  
  The United States faces a split over an important difference in policy (Constitution vs Articles of Confederation, banking and tariffs, slavery, Civil Rights)
  The parties start defining themselves over this central issue (Federalists vs Democratic-Republicans, Whigs vs Democrats, Democrats vs Republicans, Democrats vs Republicans vs Southern Democrats)
  Once a new central issue arises, either a new party springs up and subsumes one of the two existing parties, as the previous split no longer adequately defines the party coalitions, or one of the two existing parties incorporates the issue into their platform and absorbs the new party.
  
  The best example of this is the Whigs, a party that differentiated themselves from Democrats on economic grounds, but who didn't really have a reason to exist when economic differences became less important than views on slavery.
  In general, since both parties are already pretty ideologically diverse, its very difficult to make a meaningful third party run
context: The closest comparison I can think of is En Marche  ! From France, but I don’t think that would be a proper comparison.