We cannot know for certain whether they are or not.
They are automatically (if not formally) excommunicated, or excommunicated "latae sententiae" meaning "by the very commission of the offense."
Very few sins result in latae sententiae excommunication. Deliberate procurement of a complete abortion is one. Technical confusion comes in because obviously these two men have not had abortions. However, it's easy to see how inciting and publicly funding abortion when you're in a position of power could fit into the category of "a crime against human life."
So even with no formal pronouncement by the Church, obviously many, many people are walking around who have "excommunicated" themselves by their actions alone.
The excommunicated persons (we may believe Kerry and Kennedy to be so, but we have no external proof) may not receive Communion without committing a sacrilege, regardless of the priest's allowing it. This is beyond the authority of an ordinary priest.
If K&K are not excommunicated, the very least we can surely say is,they are not in a state of grace due to their sponsorship of grevious sin, and therefore also should refrain from Communion.
For anyone who has had an abortion and wishes to re-establish communion with the body of Christ, 1463 of the Catechism states:
"Certain particularly grave sins incur excommunication, the most severe ecclesiastical penalty, which impedes the reception of the sacraments and the exerecise of certain ecclesiastical acts, and for which absolution consequently cannot be granted...except by the Pope, the bishop of the place or priests authorized by them..."
Apropos of the topic of abortion, it is also a MORTAL sin (although NOT one resulting in latae sententiae excommunication!), to cast your vote knowingly for a candidate who promotes, supports, sponsors or advocates funds for abortion.
That's one of the few areas where the Church has any official position relating to democratic elections. This shows how adamant and staunch and clear is the Church's position on abortion as murder.
I don't think we disagree very much, but I would emphasize that, IIRC, differences between mortal sin and excommunication are at least two-fold:
1. The excommunicated can know for certainty, without need of deductive reasoning, that they are, in fact, excommunicated. That's the point: that the excommunicated and the community know that the excommunicated are not in communion. So if one isn't certain that one is excommunicated, it sorta defeats the point. Promoting abortion may be the moral equivalent of procuring one, but it is not the same act.
2. The excommunicated cannot simply go to the sacrament of reconciliation to be in full communion with the church, as those who are guilty of mortal sin can. They need to be accepted by the bishop.