Any publically pro-choice Catholic is excommunicated ipso facto.
Not really. It all revolves around remote material co-operation. A case can be made for such a thing but it is not officially ruled on and theologians argue on the topic. It would be argued that if they meet the necessary standards:
1. Be able to make the decision in sound mind
2. Not be forced
3. Know the penalty exists
4. Vote with the intention of furthering access to abortion
5. Do so "with hand raised" basically thumbing their nose at C law.
Then a Catholic politician would be. But again. This is always judged on an individual basis and even the current Pope...though agreeing with some Bishops decision to excommunicate and/or restrict communion to pro-choice politicians (The Mexico situation)...has not said that should be extended to all ipso facto.
The Vatican made the statement:
The thrust of the Pope's remarks, Father Lombardi said, was that politicians who support legal abortion should not receive Communion. The Pope was not declaring anyone excommunicated, he said, but the individuals who vote for abortion "have excluded themselves from Communion.
In addition:
Can. 1398 A person who procures a completed abortion incurs a latae sententiae excommunication.
Canon 1324 mitigates punishment if you did not know of the rule. But it does not remove some form of penance. Just the excommunication. Excommunication is a call to change and stop sinning. So you need to know about it or it is putative and vengeful and not in line with it's purpose.
Now the reason people argue to extend the excommunication to knowingly putting a pro-choice politician in office is canon 1329 section 2:
Accomplices who are not named in a law or precept incur a latae sententiae penalty attached to a delict if without their assistance the delict would not have been committed, and the penalty is of such a nature that it can affect them; otherwise, they can be punished by ferendae sententiae penalties.
basically those who actively vote and campaign for those who state they will further the cause of abortion are knowingly aiding and helping to extend and create the situation.
Some canon lawyers argue that all politicians who would vote on laws and further the cause of abortion are definitely subject to 1329 section 2. And I have seen canon lawyers argue that it can apply to voters as well but each situation is different.
So basically yes. Now, there is some leeway based on individual situation, intent, culpability and such.
But if someone votes for a pro-choice politician...because they are pro-choice as one of the reasons (that is important)...then yes every canon lawyer and statement I have seen would apply the automatic excommunication if the person knows the penalty exists.
Some canon lawyers (a majority) would argue it goes further. But the intention of the voter must be:
"I am voting for this person because they are pro-choice and they will further that cause."
Or something similar.
It, as all things, is case by case with circumstances we can not know to make the determination.
People should be warned that it is a reality but we should not say we know exactly that they meet the parameters of the canon law.
Now if they say: "I am a Catholic and I vote for people so they make abortions more widely available."
That is gravely wrong and seems to fit right in the wheelhouse of Canon law on this. Catholics for a Free Choice would be at this level.
It all comes down to proving this:
Accomplices who are not named in a law or precept incur a latae sententiae penalty attached to a delict if without their assistance the delict would not have been committed, and the penalty is of such a nature that it can affect them; otherwise, they can be punished by ferendae sententiae penalties.
Remote material co-operation. Not easy...and not the realm of the laity.