Donald Trump railed against immigrants in the country illegally in an often-graphic speech in Pennsylvania on Sunday, his fourth campaign stop in a month in what has become the presidential campaign's most hotly contested state.

The Republican presidential candidate called some categories of immigrants "vicious" over 10 times during his nearly two-hour address in Erie and described several violent incidents.

While there is no nationwide data on crimes committed specifically by undocumented immigrants, research shows they do not commit crimes at a higher rate than people born in the U.S.

Trump's speech was short of new policy details ahead of Election Day on Nov. 5.

Trump believes immigration is a winning campaign issue, and he has at times said he believes immigration weighs on voters' minds more than other major topics, such as the economy.

"They call them of the worst order," Trump said of immigrants who had committed violent crimes. "Charged with or convicted with heinous crimes, including child predators, drug dealers, vicious gang members, sadist thugs and people that deal in women."

At one point, he suggested he would condone a burst of police violence. "One rough hour, and I mean real rough. The word will get out and it will end immediately," he said.

It is hardly the first time that Trump has unleashed a tirade against undocumented immigrants in his bid for the White House.

In June 2015, in the speech announcing his candidacy for the Republican nomination for the 2016 election, Trump accused Mexico of sending rapists and other criminals to live in the United States.

Trump's rally Sunday in Erie came one month to the day after his vice presidential running mate, U.S. Senator JD Vance, held his own event there. Trump is due to hold another rally in western Pennsylvania, on Oct. 5.

The former president notably did not repeat his debunked claims that Haitian immigrants have eaten household pets in Springfield, Ohio. He did briefly refer to the community of Charleroi, Pennsylvania, which he has described as being overwhelmed by Haitians.

Charleroi had a population of about 4,000 in the 2020 Census. Local officials say there has been an influx of about 2,000 immigrants, including some Haitians, in recent years, drawn by work at a local food processing plant, according to NPR.

All eyes on Pennsylvania

Many allies and advisers to Trump believe Pennsylvania is the most important of the seven battleground states that will ultimately decide the election.

Of those seven, Pennsylvania is the most populous and has the most votes in the Electoral College, which in turn determines the presidential election winner.

"If we win Pennsylvania, we win," Trump said Sunday.

Democratic candidate Vice President Kamala Harris and Trump have already spent hundreds of millions of dollars on ads in Pennsylvania, more than the total spent in any other state and more per capita.

Erie County is one of two Pennsylvania counties that favored Trump in the 2016 election against Democratic candidate Hillary Clinton before favoring President Joe Biden against Trump in 2020.

Trump narrowly won the state and the presidential election in 2016, before losing both in 2020.

This time around, polls show that Pennsylvania is again competitive.

Trump's next rally in Pennsylvania, on Oct. 5, will take place in Butler, about 160 km south of Erie and the site of a failed assassination attempt on Trump in July, when a bullet grazed the former president's ear.