Well, an important thing to consider about all of this, is that if the priests and bishops do not do this, and they knowingly give these unrepentant people communion, they are also guilty of allowing them to partake in communion, and taking damnation upon themselves.
Except for two things.
1 How does a priest know if someone voted for Obama unless the person tells him and
2 Even if he knows they did he may not know if they have been to Confession or what they Confessed.
All a priest can do about this is teach, preach and warn. If a Catholic wants to take Communion with grave sin on his soul the priest cannot stop them.
High profile politicians who support abortion are a different matter. The priest is reasonably assured that this individual is using religion and has not stopped supporting a grave evil.