However, if the polls showing Clinton far ahead of Trump among Catholics are correct, it could mean big trouble for Trump, Dr. Green explained.
Catholics usually show where the general electorate stands, he said. For instance, according to Pew Research exit polls, Catholics narrowly voted for Al Gore in 2000, when he barely won the popular vote. In 2004, they voted for Bush 52-47 percent, when he won the popular vote 51-48 percent.
In 2008 Catholics voted for President Obama 54-45, when he won the popular vote 53-46 percent, and they voted for him again in 2012 50-48 percent, when he won the popular vote by that same margin.
So if Catholics really are supporting Clinton now by a wide margin, and the numbers hold until Election Day, it could suggest that Trump loses the general electorate as well, Green said.
What might be the causes of these numbers among Catholics? It "could be that Trump has done everything from insulting the Pope to talking rather callously about immigration, which matters to a lot of Catholics," he noted.
"Most Catholics are at least aware of the history of anti-Catholicism in this country, and may be somewhat unsettled by some of the rhetoric coming out of the Trump campaign about immigration."
Trump also hasn't really reached out to Catholic voters like he has to other voting groups, Green insisted.
"He's doing these appeals not based on Catholicism, Catholic values, or the Church," Green said. "He's doing them based on economic issues or fear of immigration."
"So that might happen to pull some Catholics in those areas his way, but it's a far cry from the George W. Bush strategy where you look for 'value voters' and what appeals to them. I don't get the impression that Trump is particularly interested in that," he explained.
Catholic voters as a whole are also most concerned about the same issues the general public is concerned with, according to the July Pew numbers.
When asked by Pew what issues were "very important" for them in the 2016 election, Catholics answered foremost the economy (84 percent), then terrorism (81 percent), health care (78 percent), and immigration (75 percent). Abortion and marriage were near the bottom of the list in terms of how many Catholics deemed them "very important" issues.
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"There are plenty of Catholic voters who are very religious, and religious values and beliefs matter a great deal to them," Green said.
So the decreased interest in social issues like abortion and marriage may reflect a "general" decline of interest in those issues, but it may also simply be a result of "values voters" feeling like they don't have a real choice between the two candidates, he said.