Of all the issues in the 2016 Republican presidential race, immigration has been the most influential — and not in the way party leaders want.
For years, immigration has divided conservative activists from business-oriented Republicans and the fast-growing Hispanic constituency the GOP needs more votes from to win presidential elections. But Donald Trump widened that divide — and began his rise to the top of Republican polls with hot rhetoric in his presidential announcement speech about who was crossing America's Southern border.
"When Mexico sends its people, they're not sending their best," he declared. "They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people.
"It's coming from all over South and Latin America, and it's coming probably from the Middle East," he added. "We have no protection and we have no competence, we don't know what's happening. And it's got to stop and it's got to stop fast."
To make it stop, he proposed building a wall along the U.S.-Mexico border and insisted he could make the Mexican government pay for it. He has also asserted that English, rather than Spanish, should be spoken in the U.S.
What Republican leaders fear, after a 2012 election in which President Barack Obama received 7 in 10 Latino votes, is that their presidential prospects will pay the price through further alienation.
Those fears have increased as Trump has continued to hold the lead in polls.
Business-oriented Republicans have counted on Trump's rivals to outpace him with a more temperate message. The leading fund-raiser in the GOP race, former Florida Gov. Jeb Bush, relies on a compelling personal story — his marriage to a Mexican-American he met while studying abroad.
"In 1971, eight years before then-candidate Ronald Reagan said that we should stop thinking of our neighbors as foreigners, I was ahead of my time in cross-border outreach," Bush said in announcing his candidacy. "Across a plaza, I saw a girl. She spoke only a little English. My Spanish was OK but not that great. With some intensive study, we got that barrier out of the way in a hurry.
"It has been a gracious walk through the years with the former Columba Garnica de Gallo," Bush concluded. "As a candidate, I intend to let everyone hear my message, including the many who can express their love of country in a different language."
Pressure from conservatives has forced Bush to temper his views on immigration just the same. He once favored a "path to citizenship" for the 11 million undocumented immigrants in the U.S. Now, he favors only a path to "legal status" instead.
An even more striking shift has come from Sen. Marco Rubio of Florida, the son of Cuban immigrants. In 2013, as Republican leaders urged a reconciliation with Latino voters, Rubio helped push through the Senate a bipartisan immigration bill providing a path to citizenship. But it was killed in the more conservative House, and Rubio drew fierce criticism from the right. He himself has now renounced the bill as politically unachievable.
Yet Rubio still holds promise, through his biography and hopeful tone, of repairing the breach with Hispanic voters.
"If we reform our tax code and reduce regulations and control spending and modernize our immigration laws and repeal and replace Obamacare," he said in his announcement speech, " the American people will create millions of better-paying modern jobs."
He offered his agenda in the name of "the single mother who works long hours for little pay so her children don't have to struggle the way she has to, the young student who takes two buses before dawn to attend a better school halfway across town, the workers in our hotel kitchens, the landscaping crews in our neighborhoods, the late-night janitorial staff that clean our offices, and even the bartenders who tonight are standing in the back of a room somewhere in America."
"If their American dreams become impossible, we will have just become another country," he said. "But if they succeed, this 21st century will also be an American century."
The messages of Rubio and Bush, pitted against the more bracing rhetoric of Trump and other candidates, frames an important backdrop for the CNBC debate on Oct. 28.