I haven’t spoken publicly until now as to who I would vote for.
The sentence should actually read like this:
I haven’t spoken publicly until now as to whom I would vote for.
Why? Because the subject of the dependent clause “as to whom I would vote for” is I, and whom is the object of the preposition for.
By the way, don’t worry about the outdated rule against ending a sentence in a preposition, which The Chicago Manual of Style describes as “an unnecessary and pedantic restriction” and “an ill-founded superstition.”
Questions? Comments? Let me hear from you.
Tara’s Writing Studio