There is a conflict between the position of the USCCB, and that of Cardinal Burke, on voting ethics.

The USCCB position:
Forming Consciences for Faithful Citizenship
A Call to Political Responsibility from the Catholic Bishops of the United States

“34. Catholics often face difficult choices about how to vote. This is why it is so important to vote according to a well-formed conscience that perceives the proper relationship among moral goods. A Catholic cannot vote for a candidate who takes a position in favor of an intrinsic evil, such as abortion or racism, if the voter’s intent is to support that position. In such cases a Catholic would be guilty of formal cooperation in grave evil. At the same time, a voter should not use a candidate’s opposition to an intrinsic evil to justify indifference or inattentiveness to other important moral issues involving human life and dignity.”

“35. There may be times when a Catholic who rejects a candidate’s unacceptable position may decide to vote for that candidate for other morally grave reasons. Voting in this way would be permissible only for truly grave moral reasons, not to advance narrow interests or partisan preferences or to ignore a fundamental moral evil.”
http://www.usccb.org/faithfulcitizenship/FCStatement.pdf (PDF)

So the USCCB teaches the faithful that they may vote for a pro-abortion candidate, despite (not because of) that candidates position on abortion, on the basis of other morally grave issues.

A related document, the Bulletin Insert based on the above-quoted document, has a nice summary on this question:

“As Catholics we are not single-issue voters. A candidate’s position on a single issue is not sufficient to guarantee a voter’s support. Yet a candidate’s position on a single issue that involves an intrinsic evil, such as support for legal abortion or the promotion of racism, may legitimately lead a voter to disqualify a candidate from receiving support.”
http://www.faithfulcitizenship.org/docs/insert_2p_bw_english.pdf (PDF)

The idea that abortion is the sole issue that determines our moral voting is not the teaching of the USCCB. If one candidate is pro-abortion and the other candidate is pro-life, that one issue does not compel the Catholic voter’s choice. If a candidate is pro-abortion (abortion is intrinsically evil), this may possibly lead the voter to disqualify the candidate from receiving his vote — but the document only says ‘may’.

A contrary position is taken by Cardinal Burke:
From an interview with Cardinal Burke at http://www.catholicaction.org/

“Is it ever licit for a Catholic to vote for a pro-abortion candidate….?”

“No, you can never vote for someone who favors absolutely what’s called the right to choice of a woman to destroy human life in her womb, or the right to procure an abortion. You may in some circumstances, where you don’t have any candidate who is proposing to eliminate all abortion, choose the candidate who will most limit this great evil in our country. But you could never justify voting for a candidate who not only does not want to limit abortion, but believes that it should be available to everyone.”

“And I think that if most people would reflect in this way, simply in terms of the golden rule, that they would understand that, no, it can never be right, no matter what good that I’m trying to achieve by voting for a candidate who favors that good, but at the same time favors the intrinsic evil, the grave evil of abortion, I can never justify that, voting for that candidate.”

Notice that he allows that Catholics may vote for a candidate who will only limit abortion, if there is no candidate who will entirely eliminate abortion. He allows the same type of vote in his pastoral letter (41-42). But he explicitly states that one may never vote for a candidate who favors absolutely the so-called right to abortion. So if two candidate both favor absolutely the so-called right to abortion, he does not allow a vote for either candidate. Neither does he allow for the possibility — permitted as moral by the USCCB — of voting for the pro-abortion candidate, over the pro-life candidate, because of the moral weight of a range of other grave moral issues.

In his pastoral letter, Cardinal Burke at first seems to agree with the USCCB position, since he states: “In certain circumstances, it is morally permissible for a Catholic to vote for a candidate who supports some immoral practices while opposing other immoral practices.” (n. 38)

But then he adds a provision which absolutely prohibits using this type of balanced judgment when the immorality is one of several intrinsically evil acts that he lists:

“But, there is no element of the common good, no morally good practice, that a candidate may promote and to which a voter may be dedicated, which could justify voting for a candidate who also endorses and supports the deliberate killing of the innocent, abortion, embryonic stem-cell research, euthanasia, human cloning or the recognition of a same-sex relationship as legal marriage.” (n. 39)

The Catholic voter must choose which of these two teachings, that of the USCCB or that of Cardinal Burke, to follow. Each teaching is non-infallible.

My position will be stated in a later post.