Biden is a practicing Roman Catholic, and if elected, he would be only the second Catholic to become President of the United States; John F. Kennedy was the first in 1960. Biden regularly attends mass and has spoken about how his faith helped him cope after the death of his first wife and infant daughter in a 1972 car crash, and losing his son Beau five years ago to brain cancer.

Sister Simone Campbell leads the "Nuns on the Bus," a group of politically active nuns who have been advocating for liberal policies since at least 2012. They are urging Catholic voters not to cast a ballot for Trump because they say his "policies and demeanor violate every tenet of Catholic social teaching."

Campbell is the executive director of NETWORK Lobby for Catholic Social Justice, a group that recently told its members, "Catholics cannot be true to their faith and vote for Donald Trump in November." The statement was the first of its kind in the group's nearly 50-year history. More than 50 nuns are part of the "Nuns on the Bus" campaign, which is hosting virtual events in 56 swing state communities.

Campbell said Trump's immigration policy, his mishandling of the coronavirus pandemic and his efforts to take away health care protections from Americans with pre-existing conditions, make the choice this November a "moral issue, and therefore we had to stand up."

She quoted Pope Francis: "A good Catholic meddles in politics."

Campbell said Catholics, like most voters, "worry about health care, they worry about the economy, they worry about staying well in this Covid-19 crisis, and they worry about caring for those who are at the margins of our society."

In the group's recent kickoff of their virtual bus tour to battleground states, Campbell said "for too long, Catholics have been pigeon-holed as if they only cared about" abortion.

A recent Pew Research Center poll shows White Catholics prefer Trump over Biden by eight percentage points -- 52% say they would vote for Trump or are leaning toward Trump, and 44% favor Biden. But that gap has narrowed significantly since August, when Pew put out a poll that showed Trump was 19 points ahead of Biden (59% to 40%).

Among Hispanic Catholics, Biden is the preferred candidate, with 67% saying they would vote for Biden or are leaning toward voting for the former vice president, compared to 26% for Trump.

John Carr, the founder and director of the Initiative on Catholic Social Thought and Public Life at Georgetown University, told CNN that he believes "the call to consider character and integrity are weighing heavily on Catholics" this election. Carr is a former longtime church official who helped write the document put forward by The United States Conference of Catholic Bishops on political responsibilities of Catholics.

Carr describes himself as a "pro-life, social justice, consistent-ethic Catholic" and said he is voting for Biden this fall. He decided to make his vote public for the first time in his career because he says "the stakes are too high" this election, and he wanted to provide an example to his students of using "the resources of our faith and the opportunities for democracy to make things better."

He spoke about Latino families in his parish who have been affected by Trump's immigration policies and will not vote for the President, and African American families who he says are "not going to vote for a president who fans the flames of racism." He said Trump has "failed to demonstrate the character, the integrity, the competence and commitment to the values of Catholic social teaching that merits reelection."

Several battleground states that Trump won in 2016 have a significant percentage of adults who are Catholic: 25% in Wisconsin, 24% in Pennsylvania, 18% in Michigan and 21% Florida.

Cathleen Kaveny, a professor of theology and law at Boston College, warned against looking to abortion as an indicator for how Catholics would vote in November.

"Abortion is not the main issue that Catholics vote on or that Americans vote on," she said. Kaveny noted Catholics are a diverse constituency and are split along racial, economic and educational lines "more or less the same way the country is."

"The Supreme Court's about far more than abortion," Kaveny said, adding that she believes the battle over confirming Trump's nominee is "likely to divide Catholic voters even more."

"The people who want to restrict abortion also want to undermine and dismantle the Affordable Care Act, for example, which is not consistent with Catholic teaching and which arguably has done more providing women with crisis pregnancies the support they need to reduce abortions than any kind of broader law against the topic or criminalization of it could ever do," Kaveny said.

But some groups are doubling down on the abortion messaging. The conservative group CatholicVote recently announced a $9.7 million campaign against Biden targeting Catholic voters in six swing states: Pennsylvania, Michigan, Wisconsin, Arizona, Florida and North Carolina.

"We believe a Biden presidency represents an existential threat to Catholics and to the country," CatholicVote President Brian Burch told CNN.

The group released a digital ad that knocks the Democratic nominee: "Joe Biden would force American Catholics to pay for abortions, sacrificing his Catholic values to kneel before the leftist mob." The campaign kicked off with a $350,000 digital ad buy in Pennsylvania and Michigan, according to the group.

Biden's deputy national political director, John McCarthy, told CNN that he believes Biden is "well-poised to make huge inroads and ultimately win the Catholic vote."

The Biden campaign recently announced three new ads focused on Biden's faith and values, one specifically geared towards Catholics, that will be playing on faith-based TV and radio programs in battleground states.

McCarthy said a core message of Biden's campaign is morality, and that faith voters will be looking at the "stark moral contrast between what Joe Biden and Kamala Harris are fighting for and what Donald Trump and his administration have stood for."

Biden frequently frames the November election as a "battle for the soul of our nation," quotes Pope John Paul II in his campaign ads and regularly wears his late son's rosary on his wrist.

"I think Catholic voters are looking for a vision for someone who can ultimately bring people together," McCarthy said. He noted Catholic voters are nuanced and holistic, and are focused on issues like jobs, health care, the economy and the response to the Covid-19 pandemic.

Biden's national faith engagement director, Josh Dickson, told CNN that Catholic outreach is something that the campaign has poured significant resources into. The campaign recently launched "Catholics for Biden," and there is a concerted effort to engage with Catholic voters in key swing states like Pennsylvania, Ohio, Wisconsin and Michigan, Dickson said. Campaign efforts include "listening sessions with Catholic leaders and theologians" and targeting Catholic voters with phone banks. 

Mark Shriver, a leader of "Catholics for Biden," said Catholics are "looking for commitment to decency, to humility, to taking care of our common home, the environment, as well as taking care of our fellow human beings."

"I think that is the message that is resonating," Shriver said.

Trump 2020 deputy campaign manager Justin Clark told CNN that the "contrast couldn't be more clear" between Trump and Biden. He described Trump as "the most pro-life president in history, a vocal defender of religious liberty, and has appointed over 200 judges to the federal bench."

In their outreach to Catholic voters, the Trump campaign is focusing its messaging on pro-life issues, judicial appointments and "religious freedom." The campaign says it has hired Catholic coordinators in key swing states of Wisconsin and Pennsylvania, and earlier this year launched "Catholics for Trump."