What about Catholics who vote for these pro-abort politicians? Are they also excommunicated? I know you can’t prove who someone voted for, but are they technically immune?
I wouldn't think they would be, because a lot of the time your only choice is between 2 or more politicians who are pro-abortion. In that case, you'd vote for the lesser of two (or more) evils. Chances are one of the candidates isn't as gung ho about abortion as the others, such as wanting to allow some kinds of abortion but not have it be a free-for-all.
The Vatican has already commented that it is better for a Catholic to vote in an election where there is no pro-life candidate than to simply abstain from voting altogether.