In much of the rest of the world a Political Party is a Movement unlike the loose US Parties.
In other countries a bloc of voters support the movement but don’t nominate or vote for their country’s equivalent of President [4]
The Prime Minister of Britain, the President of Israel, the Chancellor of Germany[1] are all their Party/Movement Chair [2]. The Chair is elected by the Party members. In most cases “ membership” involves a lot more than simply registering for that Party.
The Chairperson becomes the equivalent of President by forming a coalition of multiple Party/Movements and being elected in the Lower House of the Legislature. Our equivalent of the Speaker of the House.
Other countries Party/Movements represent tangible Ideals/Goals of a Mass Movement. More like a US Labor movement. Rather than the US model of intangibles of...idk...? Can you say what your Party stands for? Other than vaguely?
A US Party has to encompass close to 50% of the voters so how can it represent anything but...a vagueness somewhat acceptable to a wide spectrum of interests?
The Trump and Sanders movements largely have determined they do NOT want to part of the old-style US political parties. Are willing to sit out the November election in order to disrupt the status quo.
In that respect they mirror what does work in the rest of the world. [3]
Perhaps the Trump and Sanders blocs are the wave of the future rather than aberrations.
===========FOOTNOTES============
[1] Angela Merkle is the Chancellor of Germany, The German President is elected by popular vote and is technically head-of-state. Ever heard of Frank-Walter Steinmeier, the current President?
[2] The Prime Minister does not have to be Party Chair. Most famously, PM Winston Churchill who had spent 20 years as a backbencher. Also he was kicked out by his Party the second the war ended.
[3]. The Founders feared an overly strong President far more than they feared a disjointed tumultuous yelling-screaming-dueling Congress. But the Founders were all Rich.
Our broader Class Culture has a preference for Lone Wolves/Rugged Individuals not tied to Property. So we are less interested in following Movements as one-of-many. Our preference is for the Man on the White Horse. Why US Labor movements have been strong only when there are a lot of recent immigrants as members?
[4] FRANCE: Direct election for President by popular vote in 2-3 rounds. HOWEVER, their pre-requisites include Financial statements and the Candidate obtaining petition signatures hundreds of elected officials. Difficult except for Party chairs.