1. The "Catholic" politician who materially supports abortion by, say, resisting the outlawing of abrtion or by supporting gummint funding of abortion has, according to Canon Law, committed a mortal sin.
2. All that is necessary to excommunication is the unrepented commission of mortal sin (must be grave matter, must be known by the sinner to be grave matter, must nevertheless be chosen by the sinner). Contrary to widespread error, all excommunications are not showy public affairs with lots of publicity. In fact, very few are.
3. Today's bishops (successors to the apostles) are not immune from mortal sin. See Judas who is the behavioral ancestor of all too many of them.
4. St. John Chrysostom famously observed that the floor of hell is paved with the skulls of bishops.
5. One way for a bishop to commit a mortal sin and to excommunicate himself is to give the Holy Eucharist to be consumed by the pro-abort likes of Traitor John Kerry, Ted the Swimmer Kennedy, Rosa "Emily's List Executive Director" DeLauro, Face Lift Pelosi, et al.
6. It is hard to imagine such bishops as being truly in communion with the Bishop of Rome, even if he takes no action against them.
Penultimately, consider that Rome and B-XVI are engaged in a campaign of re-Catholicizing AmChurch by attrition. Most recent American appointments to bishoprics have been very much more Catholic than their rebellious predecessors.
Finally, of course, God bless you and yours, Jim, and may God and B-XVI send to New Hampshire a Catholic bishop (for a change) with an attitude and soon.
It may be so that many politicians, "thinking Catholics", "seamless garment but still pro-death" Catholics, and all their bishops (those whose skulls are not paving the floor of Hades already) have been invisibly excommunicated already.
I hope so.
But it is in the nature of a visible hierarchy which desires to be seen as in authority that public acts matter.
Giving Holy Communion to Kennedy matters, because of the effect on all of this who witness the act.
Kennedy's hypothetical private and invisible excommunication does not matter, now because no one knows, and later because "It is written: " 'As surely as I live,' says the Lord, 'every knee will bow before me; every tongue will confess to God.' " So then, each of us will give an account of himself to God." (Romans 14:11-12).
Invisible excommunications which do not exclude the invisibly excommunicated from the Eucharist are unnecessary, per Romans.
It would be better, IMVHO, for the swimmer and all of his buddies to get the boot.