The following comes from remarks by Bishop Robert McElroy at University of San Diego on November 1, on the San Diego Diocese website:

The contrast between the beautiful vision of politics that Pope Francis presented while speaking to a joint session of Congress last year and the political campaigns that have unfolded in recent months could not be more heartbreaking.

I speak to you tonight as a bishop who is part of a long tradition in Catholic episcopal leadership in the United States which holds that both the Church and society are best served when bishops refrain from publicly endorsing or favoring, either directly or indirectly, specific candidates in partisan elections.  This tradition stretches back to John Carroll, the first bishop in the United States. It is reflected in the consistent practice of the United States Conference of Catholic Bishops which issues its moral principles for guidance in presidential elections a full year before the elections itself, so as to ensure that the bishops will not be seen as tailoring their teachings to favor particular candidates.

It is sometimes said that this tradition of neutrality in partisan elections springs from the tax status of the Church, or from a desire to avoid divisiveness within Catholic communities. But in reality its foundation is far deeper.

It is a core teaching of Catholic ecclesiology that the sanctification of the world falls primarily to lay women and men. And it is a core teaching of Catholic moral theology that it is deeply within the conscience of the individual believer that key moral decisions must be made. The foundational assertion of democracy is that the average citizen is best equipped to guide society through electoral choice.

The corollary within Catholic teaching which supports the democratic impulse is the proposition that in discerning which candidate will best advance the common good, the prudential decision of each citizen remains paramount. Thus while bishops must teach on principles of moral judgment, and outline key elements of the common good which are at stake in a particular historical moment, they should refrain from favoring particular candidates.