Answer:
No single person is in charge of the party.
Step-by-step explanation:
Major American poltical party such Democratic party and Republican party has Party Organization, which defines the formal structure of the political party, its active members and the leadership. The leadership of the party are responsible for coordinating party behavior and supporting party candidates.
The party's National Committee from the Party's Organization is saddled with various responsiblities, among which is planning and carrying out primary election timetables and conducting primary election.
Hence, it is the Party Organization and not a single person that is in charge of Major American party.