Since the earliest days of his presidential campaign, President Donald Trump has inflamed tensions over race and immigration.

As he escalates his rhetoric, cracks down on the border, and restricts legal immigration, new polling shows Republican voters are expressing increasingly anti-immigrant views.

A July Pew survey found that 57% of Republicans and right-leaning independents believe that if the US is too open to immigrants "we risk losing our identity as a nation" — a 13 percentage point increase over the last two years.

"For a certain segment of the GOP electorate, it reaffirms why they support Trump," Jonathan Metzl, a professor of sociology and psychiatry at Vanderbilt University, told INSIDER of Trump's anti-immigrant rhetoric.

The rightward shift on immigration among Republicans is compounded by a "backlash effect" among Democrats, who've grown more progressive on racial issues and immigration, Duke professor Ashley Jardina told INSIDER.

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At a Wednesday night rally in North Carolina, President Donald Trump called four progressive congresswomen of color "hate-filled extremists who are constantly trying to tear our country down," and repeated his request that they leave the US.

Trump singled out Rep. Ilhan Omar, a US citizen who came to the country a child refugee from Somalia, accusing her of sympathizing with terrorists.

Then the crowd broke out into a chant, "Send her back! Send her back!" and Trump paused for 13 seconds, letting the shouts grow. On Thursday, Trump said he "was not happy with" the episode, despite prompting the sentiment by telling the congresswomen to "go back" to their "crime infested" countries.

Since the earliest days of his presidential campaign, Trump has inflamed tensions over race and immigration. As he escalates his rhetoric, cracks down on the border, and restricts legal immigration and asylum seekers' entry, new polling shows Republican voters are expressing increasingly anti-immigrant views.

Read more: Alexandria Ocasio-Cortez tells Trump he has a 'racist heart in his chest' after he denies having a 'racist bone in my body'

A July Pew survey of 1,502 adults found that 57% of Republicans and right-leaning independents said they believe that if the US is too open to immigrants "we risk losing our identity as a nation" — a 13 percentage point increase compared to their responses when the same question was posed two years ago.

Meanwhile, Democratic support for American openness to immigrants has remained steady at around 85%.

Experts say the sharp uptick in anti-immigrant sentiment among conservative voters is likely at least in part due to Trump's rhetoric and policies.

"There's very little else that would explain such a sharp increase" in anti-immigrant sentiment, Lee Drutman, a senior fellow at the New America Foundation, told INSIDER. "Most public opinion follows from political leaders ... and we've seen Trump making a lot of disparaging comments about immigrants and he's really set the tone."

According to a Reuters/Ipsos poll, Trump's approval rating among Republicans rose by 5 percentage points to 72% after his racist tweets last weekend targeting the four congresswomen.

More broadly, Ashley Jardina, a professor at Duke University and author of "White Identity Politics," has found that Republicans and Democrats are increasingly divided both along lines of race and attitudes toward race.

"The consequence of this sorting is that many Republicans are either unlikely to find Trump's rhetoric offensive, or they are likely simply to agree with it," Jardina told INSIDER.

She's found that white Americans who feel a strong attachment to their racial group are more likely to support Trump, consider illegal immigration the biggest issue facing the country, and feel negatively about the growth of non-white populations in the US.

A January Pew poll of 1,505 adults similarly found that Republicans and Democrats have never been more divided in their feelings toward immigration.

Read more: Pence's chief of staff defends Trump's racist tweets, becoming the first White House official to comment on them

While 83% of Democrats said immigrants "strengthen the country because of their hard work and talents," just 38% of Republicans said the same. And while 11% of Democrats said immigrants "burden the country by taking jobs, healthcare, and housing," 49% of Republicans called them a burden.

The rightward shift on immigration among Republicans is compounded by a "backlash effect" among Democrats, who've grown more progressive on racial issues and immigration, Jardina said.

The July Pew poll found women, black people, people under 30, and those with college degrees were significantly more likely to believe America's openness to people from around the world is "essential to who we are as a nation."

And Drutman found in a study after the 2016 election that voters who supported President Barack Obama and then voted for Trump are more conservative on race and immigration issues.

"For a certain segment of the GOP electorate, it reaffirms why they support Trump," Jonathan Metzl, a professor of sociology and psychiatry at Vanderbilt University, told INSIDER of Trump's recent comments. "He identifies a threat, he tells people, 'I'm gonna be the person who's gonna protect you.'"