Here, briefly, is my position on the question of pro-abortion politicians and the Eucharist:
To begin with, whoever acts in formal or proximate material cooperation with legalized abortion should not present himself for Communion.
That said, whether a particular person who presents himself for Communion is to be denied on the basis of imputed formal or material cooperation with legalized abortion is a matter of prudential judgment, not Church precept or canon law. A bishop has the authority to make this judgment for the Masses celebrated within his jurisdiction.
The above paragraph contains two concepts I think are often mangled. The first is of something being "a matter of prudential judgment." Being a matter of prudential judgment doesn't mean that the thing is a matter of moral indifference, that an objectively wrong decision can't be made, much less that a viciously immoral decision cannot be made. Intentionally or not, prudence can fail in matters of prudential judgment in ways similar to ways justice can fail in matters of judicial judgment. But it does mean there's no law that can be cited to determine fully what must be done. A matter of prudential judgment is a classic example of the incompleteness of rule-based morality.
The second concept a lot of people seem to mangle is that of episcopal authority. That doesn't merely mean the bishop is the one who gets to make the rules; again, rule-based morality is inadequate. The bishop's authority is apostolic, and the Christian faithful reject that authority at the risk of rejecting the authority of the Apostles, which was given to them by Christ.
Rejecting authority takes many forms that fall short of explicitly denying that the bishop has it. Lumen Gentium goes to far as to say that "the faithful must cling to their bishop, as the Church does to Christ, and Jesus Christ to the Father, so that all may be of one mind through unity, and abound to the glory of God." I don't think the claim that some Catholics today fail to cling to their bishop as the Church does to Christ is very controversial.