Let me give you a scenario..
Would you vote for a candidate who was pro-life, but also pro-slavery?
What would a Catholic do in this instance?
Yes, *if* the other candidates were worse. If another candidate was pro-abortion but anti-slavery, the right choice would still be the pro-life candidate, ceteris paribus, because murder is a greater evil than slavery.
- A8
"... Pope Paul III applied the same principle to the newly encountered inhabitants of the West and South Indies in the bull Sublimis Deus (1537). Therein he described the enslavers as allies of the devil and declared attempts to justify such slavery "null and void." Accompanying the bull was another document, Pastorale Officium, which attached a latae sententiae excommunication remittable only by the pope himself for those who attempted to enslave the Indians or steal their goods.
"When Europeans began enslaving Africans as a cheap source of labor, the Holy Office of the Inquisition was asked about the morality of enslaving innocent blacks (Response of the Congregation of the Holy Office, 230, March 20, 1686). The practice was rejected, as was trading such slaves. Slaveholders, the Holy Office declared, were obliged to emancipate and even compensate blacks unjustly enslaved.
"Papal condemnation of slavery persisted throughout the eighteenth and nineteenth centuries. Pope Gregory XVI's 1839 bull, In Supremo, for instance, reiterated papal opposition to enslaving "Indians, blacks, or other such people" and forbade "any ecclesiastic or lay person from presuming to defend as permissible this trade in blacks under no matter what pretext or excuse." In 1888 and again in 1890, Pope Leo XIII forcefully condemned slavery and sought its elimination where it persisted in parts of South America and Africa."
The answer is that a practicing Catholic could not in good conscience vote for a person who endorses slavery. Whatever else that candidate supports or does not support is immaterial.