Regarding the controversy over Holy Communion and one's abortion stance (as well as one's stance on some other issues), it is helpful to remember some things already said. For example, this six-point 2004 Memorandum from (then) Cardinal Ratzinger, as Prefect of the Congregation for the Doctrine of the Faith, to Cardinal McCarrick, then head of the U.S. bishops' task force on Catholic politicians:
1. Presenting oneself to receive Holy Communion should be a conscious decision,
based on a reasoned judgment regarding one’s worthiness to do so, according to
the Church’s objective criteria, asking such questions as: "Am I in full
communion with the Catholic Church? Am I guilty of grave sin? Have I incurred a
penalty (e.g. excommunication, interdict) that forbids me to receive Holy
Communion? Have I prepared myself by fasting for at least an hour?" The practice
of indiscriminately presenting oneself to receive Holy Communion, merely as a
consequence of being present at Mass, is an abuse that must be corrected (cf.
Instruction "Redemptionis Sacramentum," nos. 81, 83).
2. The Church teaches that abortion or euthanasia is a grave sin. The Encyclical
Letter Evangelium vitae, with reference to judicial decisions or civil laws that
authorize or promote abortion or euthanasia, states that there is a "grave and
clear obligation to oppose them by conscientious objection. [...] In the case of
an intrinsically unjust law, such as a law permitting abortion or euthanasia, it
is therefore never licit to obey it, or to 'take part in a propaganda campaign
in favour of such a law or vote for it’" (no. 73). Christians have a "grave
obligation of conscience not to cooperate formally in practices which, even if
permitted by civil legislation, are contrary to God’s law. Indeed, from the
moral standpoint, it is never licit to cooperate formally in evil. [...] This
cooperation can never be justified either by invoking respect for the freedom of
others or by appealing to the fact that civil law permits it or requires it"
3. Not all moral issues have the same moral weight as abortion and euthanasia.
For example, if a Catholic were to be at odds with the Holy Father on the
application of capital punishment or on the decision to wage war, he would not
for that reason be considered unworthy to present himself to receive Holy
Communion. While the Church exhorts civil authorities to seek peace, not war,
and to exercise discretion and mercy in imposing punishment on criminals, it may
still be permissible to take up arms to repel an aggressor or to have recourse
to capital punishment. There may be a legitimate diversity of opinion even among
Catholics about waging war and applying the death penalty, but not however with
regard to abortion and euthanasia.
4. Apart from an individual's judgment about his worthiness to present himself
to receive the Holy Eucharist, the minister of Holy Communion may find himself
in the situation where he must refuse to distribute Holy Communion to someone,
such as in cases of a declared excommunication, a declared interdict, or an
obstinate persistence in manifest grave sin (cf. can. 915).
5. Regarding the grave sin of abortion or euthanasia, when a person’s formal
cooperation becomes manifest (understood, in the case of a Catholic politician,
as his consistently campaigning and voting for permissive abortion and
euthanasia laws), his Pastor should meet with him, instructing him about the
Church’s teaching, informing him that he is not to present himself for Holy
Communion until he brings to an end the objective situation of sin, and warning
him that he will otherwise be denied the Eucharist.
6. When "these precautionary measures have not had their effect or in which they
were not possible," and the person in question, with obstinate persistence,
still presents himself to receive the Holy Eucharist, "the minister of Holy
Communion must refuse to distribute it" (cf. Pontifical Council for Legislative
Texts Declaration "Holy Communion and Divorced, Civilly Remarried Catholics"
, nos. 3-4). This decision, properly speaking, is not a sanction or a
penalty. Nor is the minister of Holy Communion passing judgment on the person’s
subjective guilt, but rather is reacting to the person’s public unworthiness to
receive Holy Communion due to an objective situation of sin.
[N.B. A Catholic would be guilty of formal cooperation in evil, and so unworthy
to present himself for Holy Communion, if he were to deliberately vote for a
candidate precisely because of the candidate’s permissive stand on abortion
and/or euthanasia. When a Catholic does not share a candidate’s stand in favour
of abortion and/or euthanasia, but votes for that candidate for other reasons,
it is considered remote material cooperation, which can be permitted in the
presence of proportionate reasons.]