Fr. Newman failed to distinguish between remote and proximate material cooperation. As you can see in
this document by then-Cardinal Ratzinger, voting for a “pro-choice” politician is
remote material cooperation, which may be justified (as Ratzinger says
explicitly with regard to abortion) by proportionate reasons.
Several U.S. bishops have expressed the prudential judgment that there are at this time no proportionate reasons to vote for a pro-choice politician (except in a case where the only likely candidates are pro-choice, in which case you choose the one who will put most restrictions on abortion). I respect their right to make such prudential judgments on this issue, as on other issues such as war, immigration, the environment, etc. But it’s important to distinguish this question of remote material cooperation from the intrinsic evil of supporting abortion itself. The two are clearly different and the difference is explicitly noted by Cardinal Ratzinger in the document to which I linked.
If Fr. Newman was expressing his pastoral, prudential judgment that no justifying proportionate causes existed, then he would be fully within his rights to do so. In fact, I would have no problem with a bishop (I’m a bit more nervous about a parish priest doing so) excluding people from communion based on such a pastoral judgment. However, it’s not clear to me that Catholic canon law actually allows for persons to be excluded from communion based on remote material cooperation. And at any rate, Fr. Newman gave the impression that he was simply stating the Church’s teaching, which he clearly was not, as you can see from comparing his statement with that of Cardinal Ratzinger.
Edwin