Donald Trump
Republican US presidential candidate Donald Trump speaks during a campaign rally in Redding, California, 3 June, 2016Reuters

Donald Trump is maintaining that US District Court Judge Gonzalo Curiel, who is presiding over a Trump University lawsuit, cannot act fairly because of his Mexican heritage and the real estate mogul's proposals to build a wall along the US-Mexico border. The presumptive GOP nominee went as far as saying that any Muslim judge would also be biased towards him because of his call last year to temporarily ban Muslims from entering the US.

"He is a member of a club or society, very strongly pro-Mexican, which is all fine," Trump told Face the Nation host John Dickerson. "But I say he's got bias. I want to build a wall. I'm going to build a wall. I'm doing very well with the Latinos, with the Hispanics, with the Mexicans, I'm doing very well with them in my opinion."

Dickerson then asked if he believed a Muslim judge would be similarly biased due to his other proposal regarding a Muslim ban. "It's possible, yes. Yeah. That would be possible, absolutely," Trump responded.

When asked about the US tradition of not judging people by their heritage or nationality, Trump quickly snapped back. "I'm talking about common sense, okay?"

"You know, we have to stop being so politically correct in this country," Trump added later in his interview. "And we need a little more common sense, John. And I'm not blaming. I'm proud of my heritage, we're all proud of our heritage. But I want to build a wall. Now, the Hispanics, many of them like what I'm saying. They're here legally. They don't want people coming and taking their jobs and taking their house and everything else. They don't want that."

According to Bloomberg, in a separate interview with CNN's Jake Tapper, Trump maintained that Curiel had been unfair in his judgements. "But he's an American," Tapper said. "If you're saying he cannot do his job because of his race, is that not the definition of racism?"

"No, he's proud of his heritage," Trump replied. "We're building a wall. He's a Mexican."

Trump's continued fight against the Indiana-born judge has some Republican leaders concerned. Both House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell have criticised the comments. Fervent Trump supporter and former House Speaker Newt Gingrich called Trump's comments against Curiel "inexcusable," The Washington Post reported.

"This is one of the worst mistakes Trump has made, and I think it's inexcusable," Gingrich said on Fox News Sunday. "If a liberal were to attack Justice Clarence Thomas on the grounds that he's black, we would all go crazy."

Congressman Tom Cole from Oklahoma, who supports Trump, told the Post that the presumptive nominee needs to "move from a primary message to more of a general election message" and "to start trying to find ways to reach out to groups he doesn't need to win, but he needs to make sure he's not annihilated among," including Latinos and African Americans.

Trump has just five primary races to go before the GOP convention in July. He has reached and surpassed the necessary 1,237 delegates needed to clinch the nomination.