I think that’s more of a gray area because the voters are not voting on abortion per se.
There is no gray area when it comes to murder. Even Criminal Law recognizes that if you facilitate murder you are an accessory to murder Therefore, a politician who publicly supports abortion is an accessory before AND after the fact.
Then they need to be.
Two greatest evils in the world right now are Islam and abortion, and oBUMa supports both of them.
“Those who have been excommunicated or interdicted after the imposition or the declaration of a penalty as well as others who obstinately persist in manifest grave sin are not to be admitted to communion.” Each word is significant.
"Obstinately" means they've been told beforehand and they do it anyway.
"Persist" means they've done it repeatedly.
"Manifest" means obvious, open, public.
"Grave sin" means matters of serious moral depravity --- like abortion ands infanticide --- and, incidentally, deliberately carrying out acts of war which intentionally destroy "cities or extensive geographical areas together with their inhabitants"--- all of which the church calls "abominable crimes."
Voting for Obama would not be such a violation, because it has never been defined by the Church as a sin; because a person might have done so without actually supporting abortion per se, and because it is not "manifest" --- that is, a secret ballot is not a public scandal.
Every person has the duty to refrain from Communion if they are conscious of ANY grave sin, --- any grave sin, even one which is quite private and secret.
Canon 915 specifically addresses the duty of the Bishop or priest (or, I would say, even a layperson distributing Communion), to refuse Communion to public unrepentant sinners. An example would be some of those flamboyant gay protestors who sometimes turn up for Mass with the obvious ("manifest") aim of sacrilegious reception.