Commentators who were respected, card-carrying evangelical Protestants as of June 16, 2015 (when Donald Trump announced) are saying their movement faces a “crisis” and its very name should be shelved as too politicized, at least in the U.S. A few celebrities unite with multitudes of grass-roots voters in linking evangelicalism with the Donald Trump-ified Republican Party.

Yet there are many non-partisan leaders like the Rev. Leith Anderson, who’s retiring after 13 years as president of the National Association of Evangelicals (NAE). He tells the savvy Adelle Banks of RNS that “I want the standard to be what the Bible teaches, not what the polls report.”

The media won’t be dumping the E-word any time soon. But amid the confusion and rancor, we do need to know what we’re talking about. Thus the value of the new Eerdmans paperback ”Evangelicals: Who They Have Been, Are Now, and Could Be.” This anthology of old and new articles was compiled by expert historians David Bebbington of Britain and Americans George Marsden and Mark Noll.

Self-identified evangelicals form the largest U.S. religious bloc, and the book has three potential uses for journalists. First, it could focus an analytical article. Second, it offers fine introductory background for writers who are new to this terrain. Third, those who already know a lot will learn some things.

Making definitions difficult, this fluid movement crosses denominational lines and combines formal church bodies, myriad independent congregations, “parachurch” agencies, traveling personalities, media, music and more. Some folks accurately labeled “evangelical” have other primary identities. And don’t forget the minority evangelical factions within pluralistic “mainline” Protestant denominations.

Look at things this way: Groups in councils of churches and the like have shared organizations without shared belief. Evangelicalism has shared belief without a shared organization. In defining such a loose phenomenon, journalists will be reminded of Justice Potter Stewart’s remark on pornography. “I know it when I see it.”