Josh Putnam, a University of Georgia lecturer and expert on the machinations of the parties, told me at the time that the rule at issue was Rule 9. Rule 9 reads:

“The Republican National Committee is hereby authorized and empowered to fill any and all vacancies which may occur by reason of death, declination, or otherwise of the Republican candidate for President of the United States or the Republican candidate for Vice President of the United States, as nominated by the national convention, or the Republican National Committee may reconvene the national convention for the purpose of filling any such vacancies.”

Death, declination or otherwise. No “because we want to” clause.

“Let’s be clear here: The rule is intended to fill vacancies, not to lay the groundwork for a replacement,” Putnam said. “Some have speculated that ‘otherwise’ is ambiguous. Taken out of context it is. However, under the provisions for filling vacancies, it clearly fills in any gap between death and declination (i.e.: an incapacitating illness, but one that leaves the nominee neither dead nor able to decline to run further). And that was the intention.”