Donald Trump is making America's immigration policy the top issue of his presidential campaign.

At a speech on Wednesday, Trump said illegal immigrants are responsible for many violent crimes. And he said they represent a terrorism threat to the United States.

Trump told a crowd in Arizona that illegal immigration is also an economic threat. He said it can cost Americans jobs or force them to work for lower wages.

Trump, a New York businessman, is the Republican Party's candidate for the presidency. The candidate of the Democratic Party is Hillary Clinton, a former secretary of state, senator and the wife of former President Bill Clinton. The U.S. presidential election is November 8.

Some observers expected Trump to moderate some of the positions on immigration during the Arizona speech. But that did not happen.

Trump called for a tripling of immigration agents to enforce immigration laws and remove illegal immigrants with criminal records. And he repeated his call for building a wall along the U.S. border with Mexico.

‘They Don't Know It Yet'

"We will build a great wall along the southern border," Trump said. "And Mexico will pay for the wall. One hundred percent. They don't know it yet, but they're going to pay for it."

Hillary Clinton opposes a border wall. Clinton has said she will push a bill in Congress to give immigrants without legal documentation a path toward citizenship.

Stephen Brooks is with the Ray C. Bliss Institute of Applied Politics at the University of Akron in Ohio.

He said Trump continues to appeal to voters who worry that a long-time goal of many Americans is no longer possible for them and their families. That goal is to hand down a better life for their children.

"Many believe that is out of reach and they blame -- whether fairly or not -- immigration and trade," Brooks said.

Many of these voters are white men, Brooks said. Many live in areas where factories that produced clothing, steel and other products are gone. So are the high-paying jobs those businesses provided.

White, working-class voters helped Trump surprise the experts and defeat 16 other candidates for the Republican presidential nomination.

Trump's problem is that these voters may not be enough to win a general election, with an increasingly diverse group of voters, Brooks said.

More Hispanic Voters

In 2012, 71 percent of Hispanic voters chose President Barack Obama over his Republican opponent, Mitt Romney. A public opinion survey in July found that 82 percent of Hispanic voters have an unfavorable view of Trump.

Jacob Monty is an immigration lawyer from Texas. He served on the National Hispanic Advisory Committee for Donald Trump. Monty resigned from the committee after the Arizona speech. He said the candidate's immigration positions did not match what Trump told him and other committee members.

"It's a sad day because I am no fan of Hillary Clinton," Monty told television broadcaster MSNBC.

A record 27.3 million Hispanics have the legal right to vote, according to the Pew Research Center.

Brooks said Trump is also having trouble with many white college graduates, especially women, who consider Trump's message too divisive.

Just hours before his speech, Trump traveled to Mexico City to meet with Mexican President (Enrique) Peña Nieto. The candidate used diplomatic language, saying a Trump administration would work together with Mexican leaders to secure the U.S.-Mexico border.

When he first announced his candidacy in June 2015, Trump said Mexico was sending people "bringing drugs," "bringing crime" and "rapists."

'Spectacular, Spectacular Hard-Working Poeple'

In Mexico City, Trump said Mexican-Americans are "spectacular, spectacular hard-working people."

David Damore teaches political science at the University of Nevada, Las Vegas. He said it almost seemed as if there were "two Donald Trumps" speaking on Wednesday.

For the Mexico trip, Damore said, it was Trump being civil and reaching out to an important U.S. ally. But in the Arizona speech, Trump sent a strong message to his supporters that he is not backing down from strong immigration policies and tough language, Damore said.

Writer and political commentator Ann Coulter had expressed concern that Trump was no longer calling for tough policies against illegal immigration. But she praised him after the Arizona speech.

"I hear (former British Prime Minister Winston) Churchill had a nice turn of phrase, but Trump's immigration speech is the most magnificent speech ever given," she wrote on Twitter.

But Damore and Brooks said the language Trump used in his Phoenix speech turns off many wealthy and well-educated white voters.

I'm Bruce Alpert.

Bruce Alpert reported this story for VOA Learning English. ­­­­­­George Grow was the editor.