It is on many of these issues that Catholics have raised concerns about Trump. While both major Democratic candidates – former Secretary of State Hillary Clinton and Vermont senator Bernie Sanders – are long-time abortion advocates and therefore problematic from a Catholic perspective, critiques of Trump are more nuanced.
For one, Trump's plan to deport 11 million undocumented immigrants stands in sharp contrast to the U.S. bishops' repeated call for comprehensive immigration reform that emphasizes family unity and includes an earned legalization program.
The business mogul also gained considerable attention for his assertion that "torture works" and his plan to kill the family members of terrorists. Although he later backtracked on these statements, critics voiced continuing concern over his willingness to commit war crimes and compromise human dignity.
Trump's casino was the first in Atlantic City to have an in-house strip club. And while the GOP frontrunner says he opposes same-sex marriage, he has attracted criticism from defense-of-marriage groups who note that he has bragged in the past about having affairs with other married women and has made numerous explicit and degrading statements about women.
Furthermore, his proposal for an indefinite ban on allowing Muslims into the U.S. has drawn serious concern from legal experts who say it is a flagrant violation of religious liberty, endangering the fundamental right for other faiths as well.
And while the Catechism teaches that the death penalty should be restricted to cases in which it is the "only possible way of effectively defending human lives against the unjust aggressor," Trump wants to expand the use of capital punishment, making it the mandatory penalty for killing a police officer.
While Trump currently says that he is pro-life, he made strong pro-choice statement in 1999 and 2000. A few months ago, he said that his sister Maryanne Trump Barry would be an ideal Supreme Court nominee, despite her striking down New Jersey's ban on partial-birth abortions as a judge. Several major pro-life groups have questioned Trump's commitment to the pro-life cause, saying he "cannot be trusted."
Other criticisms of Trump include what many see as disparaging comments and actions toward women, immigrants, minorities and Pope Francis.
What is a Catholic to make of all this? Moral theologians refrained from suggesting that Catholics should vote for any specific candidate, but agreed that Trump has supported many seriously troubling causes.
"The evidence is overwhelming that no Catholic who desires to be informed by the Church's teaching can vote for Donald Trump," said Pecknold.
The case against Trump is two-fold, he continued. First, Trump's platform is so "devoid" of "concrete or workable policy proposals" that it's "simply unreasonable" to guess what he would actually do once in office, he said.
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Secondly, "when it comes to the conscience," Trump's personal character and the persons or causes he has supported or received support from should be unacceptable to Catholic voters, he added.
"This is a man who, before any of his policies can be considered, should be seen as a false friend to the working class, and an enemy to the unborn, racial and religious minorities and the dignity of the human person generally," Pecknold said.
Catholics should not vote for candidates "that they know will support and promote intrinsically evil acts," Pecknold stressed. But in the event that both major candidates support intrinsic evils, Catholics must make a choice: take the "extraordinary step" of sitting out the election, vote for a third-party or write-in candidate with the knowledge that they have virtually no chance of winning, or "carefully deliberate about which candidate is less likely to pursue policies which promote intrinsically evil acts, and is more likely to achieve greater good."
Fr. Thomas Petri, academic dean at the Dominican House of Studies in Washington, D.C., added that when all available political candidates support intrinsically evil acts, "Faithful Citizenship" makes clear that the faithful are permitted to vote for the candidate whom they believe will "do less damage."
"Catholics must be careful to understand the very grave and immoral positions that Trump espouses both politically and in his personal life. If they vote for him, it cannot be because of his partisanship or because of those grave immoral positions, but because a Catholic, in good conscience, after reviewing the situation, may believe that Trump is the lesser evil of all possible candidates," Fr. Petri said.
"In this election cycle, should Clinton and Trump be the two nominees for the presidential election, Catholics must either not vote or choose one after serious and careful consideration," he continued. "We Catholics are not permitted to vote for either flippantly or as a matter of routine."