This is the reference given for  here...
Latae sententiae is a Latin term used in the canon law of the Catholic Church meaning literally “given (laid down) sentence”.
Officially, a latae sententiae penalty follows automatically, by force of the law itself, when the law is contravened. A latae sententiae penalty may be either one of excommunication, interdict, or suspension. Excommunication prohibits the exercise of certain baptismal rights, and may involve restrictions on participation in liturgical events and church governance, and the reception of church benefits. An interdict involves the same liturgical restrictions as excommunication, but does not affect participation in church governance. Suspension, which affects only members of the clergy, affects all or some acts of power of orders, governance, or functions attached to an office.
In the code of Roman Catholic canon law currently in force, there are eight instances when a person may incur excommunication latae sententiae. Unless the excusing circumstances outlined in canons 1321-1330 are verified, the following persons incur excommunication latae sententiae:
an apostate from the faith, a heretic, or a schismatic;
a person who throws away the consecrated Eucharistic species or takes and retains them for a sacrilegious purpose;
a person who uses physical force against the Pope;
a priest who absolves an accomplice in a sin against the sixth commandment (the ban on adultery) except in danger of death;
a bishop who ordains someone a bishop without a pontifical mandate, and the person who receives the ordination from him;
a confessor who directly violates the sacramental seal of confession;
a person who procures a completed abortion; and
accomplices who are not named in a law prescribing latae sententiae excommunication but without whose assistance the violation of the law would not have been committed.
Various other persons incur excommunication latae sententiae by papal decree, including:
a person who violates the secrecy of a papal election, or who interferes with it by means such as simony;
a woman who is ordained as a priest or a bishop who ordains a woman as a priest.
Some instances in which one incurs interdict latae sententiae include the following:
using physical force against a bishop;
attempting to preside at Eucharist, or giving sacramental absolution, when not a priest;
falsely denouncing a confessor for soliciting a penitent to sin against the sixth commandment; and
a perpetually professed religious who attempts marriage.
If the ecclesiastical authority notices someone incurring what it considers a latae sententiae penalty, it may declare that the person has done so. However, the punishment is in effect since the perceived fault was committed, and the declaration simply aims to ascertain what the Church considers a fact.
A latae sententiae penalty differs from a ferendae sententiae (sentence to be made) one. If one commits an ecclesiastical offense for which a ferendae sententiae punishment is prescribed, the penalty will only take effect when imposed by the competent ecclesiastical authority.
Note that latae sententiae is an adjectival phrase accompanying a noun, such as “excommunication”. In connection with a verb, the corresponding adverbial phrase is in ablative absolute form, as in: “He was excommunicated lata sententia.”
I see in there that excommunication latae sententiae obtains for those who procure completed abortions. I am made to understand that this applies as well to those who give formal assistance to a specific case of a completed abortion.
But the first question is whether pro-abortion politicians are giving formal assistance to specific acts of completed abortion. It seems to me that one can argue that rather, they are making no obstacle to abortion, rather than that they are actively assisting in the act of abortion.
For those who also believe that the government should pay for abortions, the argument that they are not actively assisting in the procurement of abortion is weakened. But for folks who merely state that the government ought not prevent abortions, the answer to the question is much less clear.
The other difficulty is the distinction between proximate cooperation and remote cooperation. It's difficult to argue that pro-abortion politicians are giving proximate cooperation to individual completed abortions. And generally, I'd always been under the impression that severe penalties in Church law usually are not imposed for folks whose cooperation with evil is remote.
Not too long ago, some Mexican bishops excommunicated Mexican legislators for voting for pro-abortion laws in Mexico. Pope Benedict was initially quoted as approving of that action. That would strongly suggest that pro-abortion “Catholic” politicians ARE excommunicated latae sententiae. (We should remember that the bishops who were claiming that these politicians were excommunicated were not affording the politicians any canonical due process - thus, any excommunication would have to be latae sententiae).
Yet, a day or so later, the official word from the Vatican was that that was not what Pope Benedict actually meant.
I think that there are other potential grounds to claim that pro-abortion “Catholic” politicians are excommunicated latae sententiae. But these other grounds, much as your suggested grounds, are speculative.
Even Archbishop Burke and other relative “hardliners” haven't suggested that these folks are excommunicated latae sententiae (at least as far as I'm aware), only that they should not be admitted to Holy Communion. And indeed, that is what then-Cardinal Ratzinger said in his letter to the American bishops in 2004 - that pro-abort politicians should be excluded from the Blessed Sacrament - NOT that they are excommunicated latae sententiae.
I think that it would be better for us to stay on the firmer ground of asserting that these politicians should be denied the Blessed Sacrament. I think the question of excommunication latae sententiae is an open question, and not within the competence of any of us here.