His prestige was somewhat marred in later life when he agreed to run as the only major candidate opposing Ferdinand Marcos in the 1981 Philippine presidential election.

Santos married Juanita Garcia of Baliuag, Bulacan in 1934 and they had eight children: Reynaldo, Edgardo, Ravenal, Lamberto, Alexis, Liberty, Daisy, and Nenita.

For his World War II activities, Santos received numerous citations and awards from the Philippine and American governments.

By 1981, Santos had mostly retired from political life, devoting his activity to veterans affairs; thus, it came as a surprise when he agreed to run for President against Ferdinand Marcos in the 1981 elections.

The elections were called shortly after Marcos lifted the nine-year-old declaration of martial law while retaining authoritarian powers at the same time, and were seen as a means of maintaining the veneer of democracy, especially in the international community.

Santos' candidacy, ostensibly under the banner of the then-moribund Nacionalista Party, provided Marcos with at least one other "major" candidate he could run against.