The party primary has nothing to do with the election, as far as who can win.
It is a private election of who the party will run as candidate.
The political parties don't even have to allow non-party members to vote in the primaries.
It is the equivalent of the election of officers in an Elk's Lodge.
Nor does the Electoral College disallow independent candidates.
Other than Nebraska and Maine, whomever wins the popular votes for a state gets all the EC votes for that state.
Prior to dropping out, Perot's poll support was 39% - compared to Bush (31%) and Clinton (29%).
Don't fall for the brainwashing that "a 3rd Party vote is a wasted vote".
Roughly 43% of eligible voters didn't bother casting ballots in 2016.
That is a potential tidal change, if a 3rd Party put in the grass roots effort to get even half of those.