It's two completely different systems.  To make this analogous with the Electoral College system, an example would be that Michigan votes 60% Romney, 40% Obama, but when the Electoral College members are elected, 12 of them are for Obama and 4 are for Romney.  And that wouldn't happen, because each party elects its own electors, whereas in the party, the party as a whole elects its electors, and they don't all have to be winner take all (although some states can be).

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