That means American culture may be moving toward a mushy, self-reinforcing idea of who evangelicals are. The term becomes not a nuanced religious concept but a flat heuristic for the idea of “politically conservative Christians.” If this is indeed how some Americans view evangelicalism, their responses to pollsters would border on meaningless — at least, in terms of measuring the relationship between religion and political leanings.

Here’s what we’ve heard about evangelical voters lately: Donald Trump, Ben Carson, and now Ted Cruz are fighting for them. Cruz says that a bunch of them are “missing” (and that he’s the man to find them). And anyone will tell you that they play a decisive role in Iowa GOP caucuses.

You can’t talk about a U.S. national election — especially the Republican side of it — without a hefty discussion of what evangelicals want. But in the hurry to answer that question, the most basic of questions gets ignored: who are evangelicals? That definition can vary from person to person, or even from pollster to pollster. And at the center of it all is a term that, for all the attention it gets, is remarkably poorly defined.

How do you define it?

Here’s how squishy the term “evangelical” is: depending on the method of measurement, more than one-third of Americans are evangelical, or fewer than one-in-10 are.

That huge range comes from the different ways pollsters and other social scientists define the term. In a lot of surveys, a pollster simply asks people how they identify, often adding on the question of whether someone has been “reborn” as a Christian: “Do you consider yourself an evangelical or born-again Christian?”

According to the Pew Research Center, around 35 percent of American adults (that is, roughly half of all Christians) consider themselves evangelical or born-again. So when reporters and politicians talk about “evangelicals,” it can sound like they’re talking about a huge chunk of the population — more than a third.

But then, other national political pollsters, like CNN/ORC, add a modifier onto most of their evangelical polling, focusing on white evangelicals. (And this is the group most pundits are talking about, particularly when it comes to Republican primary politics.)

The idea, said one survey researcher, is to avoid lumping groups with clearly distinct political ideas into one bucket.

“White evangelical protestants are some of the most reliably conservative and Republican voters in the electorate,” said Greg Smith, associate director of research at Pew. “African-American protestants, on the other hand, are some of the most strongly and consistently Democratic voters in the electorate.”

“If you didn’t look at them separately,” he added, “if you lumped them all together, you would miss a big part of the story about the connections and the interrelations of religion, race, and politics in the U.S.”

Cut that pool of evangelicals or born-agains to white, non-Hispanic evangelical Protestants only, and they account for 19 percent of Americans, according to Pew’s data.

Beyond self-identification, there are more exacting ways of defining the group. In fact, Pew has two ways of counting evangelicals. In addition to asking people to self-identify, it sometimes uses a denominational system, creating a dividing line between “evangelical” Protestant denominations, like Southern Baptists, and “mainline Protestants,” like Methodists (“historically black” Protestant churches are in a separate category). By this definition, around 25 percent of Americans are evangelical.

Definitions can get even tighter — and with them come smaller estimates of evangelicals. The Barna Group, a research firm that specializes in religious issues, uses what may be the toughest definition of evangelicalism out there. It asks a series of nine questions about beliefs (Did Jesus lead a sinless life? Does salvation come from “grace, not works”?). Only 6 percent of Americans are “evangelical” by Barna’s definition, according to their latest count.

The entanglement between race and religion

Because political polls often focus on white evangelical voters (which is in turn in part because those evangelicals — however one defines them — are such a coveted demographic among GOP voters), white evangelicals end up getting a huge amount of media attention. But that means they can end up being portrayed as the face of evangelicalism, period. Indeed, articles about this polling sometimes end up conflating white evangelicals with all evangelicals.

Anthea Butler, an associate professor of religious studies at the University of Pennsylvania, believes that race ends up getting glossed over in the hubbub over the so-called “evangelical vote,” as she said in a February speech.

“The media does this all the time. You never hear them talk about black evangelicals,” she said. “Watch the 2016 election. When they begin to talk about evangelicals again, they won’t go to Bible-believing black evangelicals. They’re going to talk to white people. I know. I’ve watched them do this, and I have argued with people about this over and over again.”

Consider an imaginary pair of evangelicals — one black, one white — who sit next to each other in the pew every Sunday. They could have the same religious beliefs. But as Smith pointed out, they’re likely to have vastly different political beliefs: the black churchgoer is more likely to vote Democratic, while the white one will lean GOP.

(Pew’s polling on black Protestants focuses on that group as a whole, not on black evangelicals themselves. But 82 percent of attendees at historically black Protestant churches identify as or lean Democratic, according to Pew, and 72 percent of black Protestant churchgoers identify as evangelical or born-again. Clearly, a huge share of black self-identified evangelicals also tend Democratic.)

All of which means something important: when evangelicalism comes into the U.S. political conversation, it’s often also a conversation about race. The racial discrepancies in the numbers suggest that identifying as “evangelical” doesn’t necessarily make a person more likely to vote Republican.

The self-definition problem

The question at issue with measuring evangelicals is the question of what people’s religious beliefs mean for their political views.

Part of the problem here is that “evangelical” has a muddled definition, even when you strip away the politics and survey research.

“The term ‘evangelical’ has a very broad set of meanings in Christianity. In its origins, it refers to the evangel, which is a Greek word from the New Testament that refers to the ‘good news,’ or the gospel of Jesus Christ,” said John Green, professor of political science at the University of Akron and an expert in the intersection of politics and religion, in an August interview.

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