Church teaching is that if you behave like Kerry, you have "excommunicated" yourself. That means, that although you go through the motions, it doesn't really count.
And since this is public, rather than private, behavior, plenty of priests wouldn't give him communion (if he was so foolish as to come to my parish, not only would my pastor refuse him communion, but he might state publically why!)- but still plenty will, either because they disagree with the teachings or don't want to cause problems.
In the great sorting out after death, God will know who was for him, who wasn't and who caused other people to fall because of bad behaviors when they were in positions of authority...
It is the rarest of things for the church to do a formal excommunication.
Another way to put it, 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.