A decade or more ago — I forget which White House race — the pollster and scholar John C. Green of the University of Akron made a witty comment about American politics and the role that faith often plays at ground level on election day.

This election, he told me (and I paraphrase), was going to be another one of those cases in which the presidency would be decided by Catholic voters in Ohio. But Green didn’t just point at generic Catholic voters. He said that the crucial factor would be whether “Catholics who go to Mass every Sunday” showed up at the polls in greater numbers than “Catholics who go to Mass once a month.”

In other words, he was saying that there is no one Catholic vote (click here for GetReligion posts on this topic) involved in the so-called “pew gap.” Catholics who go to Mass every week (or even daily) have different beliefs than those who show up every now and then.

So when a presidential candidate hires a “faith outreach director,” it’s crucial to ask (a) which group of believers the candidate hopes to rally, (b) how many of them are out there and (c) are we talking about people whose faith pushes them into action?

You can see these factors — often hidden between the lines — in a recent Washington Post story that ran with this headline: “Pete Buttigieg hires the first faith outreach director of the 2020 campaign.” There are one or two places in this piece where the Post team comes really, really close to examining the crucial faith-based cracks inside today’s Democratic Party.

The key: Is Buttigieg trying to rally religious liberals (and secularists) who already on his side or is he, like Barack Obama, attempting to reach out to centrists and liberal evangelicals? So far, the other key player in this pre-primary faith contest is Sen. Cory Booker (D-N.J.), who urgently needs support from voters in the African-American church.

So Buttigieg has hired the Rev. Shawna Foster as his faith-outreach director. What does this tell us about the Democratic Party at this stage of the contest?

Foster … has a broad imperative to talk to all religious groups. She said she thinks mainline Protestants (those who are not evangelical and tend to be more liberal, both religiously and politically) have been overlooked by political campaigns and are probably sympathetic to the religious views of Buttigieg, an Episcopalian.

Michael Wear, who led faith outreach for Obama and has pushed Democrats to talk more to religious voters, said campaigns including Buttigieg’s should explore whether mainline denominations, which are shrinking in membership and are more politically divided than evangelical churches, can mobilize voters. “The Clinton campaign missed a major opportunity” with mainline Protestants, like those who share Clinton’s United Methodist faith, he said. “There are several candidates in this batch of candidates who have the opportunity to test whether there’s enough energy, and frankly enough people, in mainline Protestantism to be a political force.”

There’s so much to unpack in what Wear said. Frankly, this is where this story needed at least two paragraphs of hard, factual material.

About what? Well, for starters, if the world of “mainline” (think “Seven Sisters”) Protestantism is basically progressive, why did Donald Trump win that sector of the voting population by 11 percent?

Also, the world of liberal Protestantism is, with a few exceptions at the local or regional level, in a state of demographic collapse. What are the numbers there? Why did Wear bluntly ask if there are “frankly enough people” in that niche to have an impact?

All of this is linked to an old question looming over all those mainstream media think pieces about progressive faith and politics: Why doesn’t the religious left have more clout in American politics?

So, who is Foster and to which choir will she preach? Does she have any potential to reach believers in centrist Catholic or even moderate evangelical pews?

Foster, a 35-year-old pastor, … has a lot in common with Buttigieg: Both are millennials, LGBT people and military veterans. “If we want to split hairs, he’s Episcopalian, and I’m Unitarian Universalist,” she says with a laugh.

In other words, Foster is to the theological left of Mayor Pete.

This leads to the second Wear statement that points toward the future, in terms of strategic gestures inside the Democratic Party.

Buttigieg might need more help appealing to voters who are less like him than Foster is, including voters of color and those who belong to more theologically conservative denominations. Wear, who is not working for a 2020 campaign, called Foster “clearly a primary selection.” …

(Wear said that if she sets up an interview for the candidate with Christianity Today, it could be taken as a sign that she’s steering him toward more traditional Christians.)

“Shawna comes out of a very progressive slice of the faith community. At this stage of the campaign, I don’t see that as a downside,” he said. “I think it’s going to be important for her to [possibly] bring on a deputy that has experiences in other faith communities, including potentially the black church or more branches of Christianity.”

Unpack these words: “Shawna comes out of a very progressive slice of the faith community. At this stage of the campaign, I don’t see that as a downside.”

In other words, Buttigieg needs the hard core Christian left at this stage of the race, where small groups of voters from small religious groups (and the crucial “Nones”) can have a major impact in key states outside, well, the Sunbelt.

When does that become a negative? Will that approach preach in other theological and cultural zip codes? With that in mind, readers will want to recall an earlier Washington Post story, discussed in this GetReligion post: “Yes, the WPost Mayor Pete visits the Bible Belt story ran several weeks ago: But it's still important.”

The bottom line: Primary clout (hello hardcore Trump evangelicals) is not the same thing as general election clout.

How does Mayor Pete (and he is not alone among Democrats) plan to reach out to Sunday-Mass Catholics, African-American Baptists, Latino Pentecostals and lots of other folks in pews?

Stay tuned.