Donald Trump’s plan to build a “great wall” along the U.S.-Mexican border has unquestionably mobilized voters since he first detailed it during his June 2015 presidential announcement. That’s due in part to his supporters, who, according to a new poll, view immigration as a “very big” problem.

Of the seven categories surveyed, immigration remained the top concern for 66 percent of Trump backers--edging terrorism out by one percent, a Pew Research Center poll found. For comparison, only about 17 percent of Clinton supporters describe immigration as a looming threat.

The poll also found a deep partisan divide when it comes to resolving immigration-related issues. An overwhelming number of Trump supporters--79 percent-- favor building a wall along the U.S.-Mexican border, while just 18 percent of them oppose it.

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Though questions have arisen about how and whether Trump would carry out mass deportations of the millions of undocumented immigrants residing in the U.S., his language on the wall has been consistent -- he’s building it, and the Mexicans are paying for it, he says.

But Republicans nationwide are split on their perception of illegal immigrants. Nearly 65 percent characterize undocumented immigrants just as “honest and hardworking as U.S. citizens,” and 52 percent say they are no more likely than permanent residents to commit serious crimes.

These Republican sentiments clash with the business mogul’s inflammatory rhetoric on Hispanics--going back to his presidential campaign kickoff, when he referred to Mexican illegal immigrants as rapists and drug offenders. And, he has also raised ethnicity as a strike against the judge overseeing lawsuits involving his now-defunct Trump university. He said the judge presiding over the case, Judge Gonzalo Curiel--whose parents were Mexican immigrants-- presented an “absolute conflict,” given that he was “of Mexican heritage.”

“I’m building a wall. It’s an inherent conflict of interest,” Trump said in a Wall Street Journal interview.

The poll, however, suggests that, when the pool of surveyors focuses on Trump supporters specifically, they are more likely to possess negative perceptions of undocumented immigrants than the average American. Fifty-nine percent of those who “strongly” endorse Trump said that undocumented immigrants are more likely than U.S. citizens to commit serious crimes.

The Pew research comes in the midst of a fiery political storm when questions are circulating whether the Republican presidential nominee is shifting his stance on deporting undocumented immigrants. Trump, however, said he will “announce something” about his stance within the next two weeks.