Reagan meets PK Dick in Purgatory

From today's New York Times, an article written about Reagan's health:

On a plane from San Francisco to Denver, Mr. Reagan told me that his mother, Nellie, had been senile "for a few years before she died" of a stroke at age 80. Mr. Reagan said he fully expected his White House doctors to check his mental status, and he pledged to resign if he became senile while in office.

If you were senile, isn't it likely you would forget the promise you made? Or how would you know you were senile if you were senile?

Oh 25th amendment, where art thou.