The main problem with this in the US is the two-party system (fascist and conservative-light). It's a zero-sum game here, and that makes people especially protective of the candidate.
The reason the two party system can't be changed, is that the people in charge of making up the rules (elected officials of both parties) don't want it to be more competitive. And the population is too politically divided and geographically dispersed to protest properly. Members of both parties will sic the police (who are thugs) on protesters.
You probably already know all this.