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it also fell upon McMahon during the early years of Carson's tenure (when the show ran 105 minutes) to host the first fifteen minutes of Tonight.
Why did it fall upon McMahons shoulders?
substituting for Carson during a week of programs that aired between July 29 and August 2, 1963, and again for two nights in October 1963.
What caused McMahon to leave The Tonight Show?
CANNOTANSWER.

Question: What was McMahons official role?
Self-contained rewrite: What was McMahons official role on The Tonight Show?