NEW YORK - The presumptive Republican presidential nominee, Donald Trump, on Friday stood by his claim that a US judge should recuse himself from hearing lawsuits against Trump University because of his Hispanic heritage. He also singled out an African-American man attending one of his rallies, calling him “my African American”.

During an interview with CNN, he was asked about why Judge Gonzalo Curiel’s ethnicity should disqualify him from hearing the case. Trump pointed to his plan to build a wall on the US-Mexico border.

“I think I’m going to do very well with Hispanics, but we’re building a wall. He’s a Mexican. We’re building a wall between here and Mexico,” Trump said. “The answer is, he is giving us very unfair rulings, rulings that people can’t even believe. This case should have ended years ago.”

Trump said Curiel, who was born in the United States to parents from Mexico, is treating him unfairly in the lawsuits that claim his defunct real estate education programmes were fraudulent. Whenasked what Curiel’s ethnicity has to do with his ability to handle the case, the business tycoon responded: “I think that’s why he’s doing it.”

“Hillary Clinton is a stiff,” Trump added when the interviewer mentioned the Democratic front-runner’s portrayal of Trump’s arguments as racist. He also said Speaker Paul Ryan, a Republican, who condemned Trump’s attacks on the judge, doesn’t know the case. “He’s of Mexican heritage, and he’s very proud of it — as I am where I come from,” Trump said of the judge.

Later in the day at a campaign rally in an airplane hangar in San Jose, California, Trump commented on the “thugs” who protested at his rally the night before, attacking several of his supporters, and began to fondly tell the story of an African-American supporter who punched a protester. He then paused mid-sentence to single out a black man in the audience before him.

“Oh, look at my African American over here - look at him,” Trump said as he pointed. “Are you the greatest? Do you know what I’m talking about?”

He then resumed telling the story about the other black man at a different rally: “Okay, so we have an African-American guy at one of the rallies a month ago. And he’s sitting there, behaving. And we had protesters inside the arena and they were dressed in a Ku Klux Klan outfit. Okay?”

Trump said that his crowd booed these protesters and their costumes started falling apart.

“This African American gets up and, man, he slugged these guys,” Trump said, as the crowd cheered. “He slugged ‘em... So when the African American cold-cocked this guy, this guy never knew what happened. Everybody thought the African American was against me and it was the opposite. He was like this great guy, military guy.”

Trump said that the “sleazy people” in media tried to make it look like “the white guy was on my side” when really it was the African-American guy who supported him. And just as Trump pledged earlier in the day to win over Hispanic voters with the promise of jobs, he vowed to do the same for black voters.

Meanwhile, US President Barack Obama condemned the violence at the Trump rally.

During a Democratic National Committee fundraiser in Florida on Friday, Obama said that there’s no room for politics that ignores opposing opinions.

“It is very important for us to remind ourselves of who we are and what is best about American democracy and not slip into some of the bad habits that currently manifest themselves in the other party,” Obama said.

“We saw in San Jose these protesters starting to pelt stuff [at] Trump supporters. That’s not what our democracy is about,” he added.

“That’s not what you do,” Obama said. “There’s no room for violence. There’s no place for shouting. There’s no room for a politics that fails to at least listen to the other side, even if you vehemently disagree. Because I believe if you’ve got the better argument, then you don’t need to do that. Just go out there and organize and persuade.” “We have tremendous African-American support,” Trump said. “The reason is: I’m going to bring jobs back to our country. We’re going to bring jobs back.”