As currently written, Canon Law does NOT include automatic excommuncation for politicians like Kennedy who continually vote to expand/fund abortions, a major loophole that Catholic laity should demand to be closed.
Canon Law
"Canon Law," the juridical law of the Roman Catholic Church, often is cited by both sides in the abortion debate--usually to make a point about the Church's moral stance. However, Canon Law is not a moral code, it is the administrative, civil, jurisdictional, procedural and penal law of the Catholic Church. It is subject to many of the same political, administrative and practical influences that shape any other body of law; while the authoritative moral teachings of the Church, per se, belong to a different forum. But, at times, it is reasonable to make moral inferences from the Canons. Still other times it may not be. Canon Law remains a somewhat esoteric and remarkable body of law, one that is rarely discussed with much understanding.
Background
Juridically, the Church is an autocracy; the pope (alone or with a council) has sole power to draft, promulgate, and rescind the laws that govern a church of c. 900 million. Since ancient times, Canon Law was a collection of active disciplinary decrees (as opposed to moral and theological pronouncements) of the popes and councils. Each law, or "Canon," was known by the first few words of its name in Latin--the Church's official language. However, in 1917, Pope Benedict XV promulgated a comprehensive codified version of the Canon Law (the "Pio-Benedictine Code" or "Code of Canon Law"). This did for Canon Law what the Restatements supposedly do for common law. In 1983, John Paul II promulgated a new Code--the one currently in force.
Historically, abortion arises in two places in Canon Law: the law of "irregularity" and the penal law. Irregularity is a canonical bar (or "impediment") to receiving or exercising holy orders (i.e. being a deacon, priest, or bishop.). Irregularities are not punishments, per se. Insanity and existing marriage are irregularities, as are homicide and apostasy. The penal law, on the other hand, is just like state criminal law, but tailored to ecclesiastical purposes.
Penal Law
The 1983 Code of Canon Law contains the following provision:
Title VI
OFFENSES AGAINST HUMAN LIFE AND FREEDOM
Can. 1397 -- One who commits homicide or who fraudulently or forcibly kidnaps, detains, mutilates or seriously wounds a person is to be punished with the deprivations and prohibitions mentioned in can. 1336 in accord with the seriousness of the offense; however, homicide against the persons mentioned in can. 1370 is punished by the penalties specified there.
Can. 1398 -- A person who procures a successful abortion incurs an automatic (latae sententiae) excommunication.
[The Latin original reads: Can. 1398 -- Qui abortum procurat, effectu secuto, in excommunicationem latae sententiae incurrit.]
An excommunication is the heaviest spiritual sanction the Church can render. So long as it is in force, it bars the excommunicated person from the church community and from receiving most of the sacraments, as well as from all public associations affiliated with the Church. An automatic (or "latae sententiae") excommunication is an especially severe penalty. The nine or so latae sententiae excommunications in the Code are reserved for use against certain things the Church particularly wants to deter, like assaulting the pope (can.1370) and priests divulging matters heard in the confessional (can.1388). Most excommunications can only follow a tribunal trial (can. 1425, §1, 2°). But latae sententiae penalties operate like a bill of attainder in that there is no "process" for their imposition--the fact that the person voluntarily performed the proscribed act, in the absence of some exception provided in the law, means the penalty is incurred. An excommunication can usually be lifted by the local bishop (the "local ordinary") and sometimes by a priest during confession (can. 1354-1357).
The 1917 Code had a similar provision:
Canon 2350, §1 -- Persons who procure abortion, mothers not excepted, automatically incur excommunication reserved to the Ordinary at the moment the crime takes effect: if they are clerics, they shall also be deposed.
Though it is clear enough the Church has always regarded abortion as a serious sin, it was not always accorded a penal sanction in Canon Law equal to that given homicide (nor is it now, see can.1397, supra).
The first papal canon, Effraenatam, that universally imposed a penal penalty of excommunication for abortion was issued by Sixtus V in 1588. It applied to all abortions and was reserved to the Holy See. In 1591, the law was modified by Gregory XIV so that the penalty would not apply when a fetus was not "animated" or "ensouled" under the Aristo-Aquinan theory of when human life begins (not before 40 days) and gave the local bishops control of these cases. This was motivated, at least in part, by the sheer volume of litigation the law had produced ("reserved to the Holy See" meant that each case had to be taken to Rome for the excommunication to be lifted). In 1869, Pius IX rescinded the animation exception. The canons of the 1917 and 1983 Codes apply to all direct abortions. Abortions incident to otherwise lawful medical care that is required to save the life of the mother (e.g. chemotherapy, hysterectomy of a cancerous uterus) are given an interpretive exception from the rule under the priciple of "double effect."
As in all penal laws there are qualifications as to who is subject to a law--Canon 1321, and following, of the 1983 Code makes such provisions.
Irregularity
From the earliest days of the Church, men who had shed human blood, no matter how justifiable or blameless the act may have been, were excluded from entering the priesthood (e.g., Decretum Gratiani by Pope Innocent I in the year 404). This traditionally embraced abortion as a form of homicide. However, in 1211, Pope Innocent III issued the decree Sicut ex, which limited the irregularity incurred from abortion to abortions involving a fetus that was not "animated" or "ensouled." This exception was subsequently abrogated as both of the modern codes have provisions that apply to all abortions (can. 985, §4 in the 1917 Code, and can.1041, 4° in the 1983 Code).