Normally I tend to avoid political stuff, concentrating on grammar and writing instead. My interest here is no exception. I like to point out any time someone uses “whom” correctly, politics or not. It’s in the third panel:
“Whom” is the object of the separable verb “vote for” even though “whom” comes first. And objects take the objective case!
This sentence has an interesting ambiguity, by the way. The verb in question is an infinitive (to vote for) and the subject of an infinitive takes the objective case in English; hence, that “whom” here could be considered the subject of the verb!