When it became clear that normal venues were too small, Donald Trump met his Mobile, Ala., flock in the ultimate Deep South sanctuary -- a football stadium.

"Wow! Wow! Wow! Unbelievable. Unbelievable," shouted the candidate that polls keep calling the early Republican frontrunner. "That's so beautiful. You know, now I know how the great Billy Graham felt, because this is the same feeling. We all love Billy Graham. We love Billy Graham."

The thrice-married New York billionaire didn't elaborate, but apparently thought he was channeling what the world's most famous preacher would feel facing a Bible Belt crowd. Participants in evangelistic crusades, however, don't bounce up and down screaming while wearing licensed merchandise and waving single-name banners.

Adjusting his red "Make America Great Again" baseball cap, Trump quoted Rush Limbaugh, mocked Jeb Bush, prophesized the demise of Hillary Clinton and shared sordid details of crimes by an illegal immigrant. He offered -- in the rain -- to prove that his legendary hair was indeed his own.

One photo went viral, showing the candidate greeting supporters in front of a homemade sign that proclaimed, "Thank you, Lord Jesus, for President Trump."

"Donald Trump comes across as a blunt, savvy, can-do man and that kind of leader has always been popular" down South, noted church historian Carl Trueman of Westminster Theological Seminary near Philadelphia. "He is the prototypical celebrity and has his own brand of populism. That seems to appeal to many modern evangelicals."

Problems arise, however, when journalists and politicos start calling Trump the "evangelical" favorite. In one much-discussed Washington Post-ABC News poll, he was leading -- in the giant Republican pack -- with 20 percent of white, evangelical, GOP-leaning voters. Other polls show similar or greater "evangelical" support, but his numbers are weaker among those who attend church once a week or more.

"If you ask why Trump's beliefs appeal to many evangelicals, then you face an old problem," noted Trueman, in a telephone interview. "If you put 12 evangelicals in a room, you are going to get 10 or 11 -- at least -- definitions of what the word 'evangelical' means."

The journalism bible -- The Associated Press Stylebook -- notes that "evangelical" the adjective has evolved, commonly becoming a noun. The term refers to a "category of doctrinally conservative Christians. They emphasize the need for a definite, adult commitment or conversion to faith in Christ. ... Evangelicals stress both doctrinal absolutes and vigorous efforts to win others to belief."

Historically speaking, it's crucial that evangelicalism is a movement of believers in a wide variety of churches and, thus, has no comprehensive set of shared doctrines, noted Nancy Pearcey, who leads the Center for Christian Worldview at Houston Baptist University.

When specific issues arise that cause division, evangelicals usually fall back on confessions, covenants or traditions in their own individual flocks. This can make it hard to find unity in painful debates, she said, reached by email. As a rule, American evangelicals are united by shared emotions, cultural experiences, a strong sense of individualism and loyalty to charismatic leaders and their causes.

"Evangelicalism arose as a renewal movement within the established churches … and therefore it was inherently opposed to structure, history, tradition, ritual and anything that could be characterized as mere 'externalism,' " she noted. When evangelicals have formed independent organizations, causes and churches "they were weak in precisely those areas."

This makes it hard, Trueman agreed, for evangelicals facing debates on issues such as same-sex marriage to decide when preachers, activists or even educational institutions have modernized their beliefs too much and, thus, no longer fit under the "evangelical" banner.

It may also make it hard for "evangelicals" to seriously evaluate the faith claims of politicians who urgently need votes in Bible Belt primaries.

"All kinds of legal and political issues will be putting new pressures on churches in this nation," he said. "At some point, simply calling yourself an 'evangelical' is not going to be enough. People are going to need clarity. …

"Our churches and our institutions are going to have to clearly state what they believe on specific issues -- such as the definition of marriage -- or they are not going to be able to stand together. The cultural ties that worked in the past are not going to be enough."