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.
I am not a Vatican lawyer. I believe that those who openly condone and have a hand in keeping abortion legal do excommunicate themselves.
You see it differently and until some action is taken, we really don’t know the answer.