Republican presidential candidate Donald Trump speaks as New Jersey Gov. Chris Christie looks on during a new conference in Fort Worth on Friday. (LM Otero/AP)

On Sunday, Donald Trump doubled down on his accusation that a judge presiding over a lawsuit involving the billionaire's controversial Trump University is biased because he is Hispanic.

"I think the judge has been extremely hostile to me," Trump told Chris Wallace in an interview on "Fox News Sunday." "I think it has to do with the fact I'm very, very strong on the border, and he happens to be extremely hostile to me. We have a very hostile judge. He is Hispanic, and he is very hostile to me."

The now-defunct Trump University was a real estate training program that started in 2004 and has come under fire both in courts and on the campaign trail because some students deemed it a scam. 

By way of background, here's The Post's Jenna Johnson

About 80,000 people attended free introductory seminars held in hotel ballrooms across the country. About 9,200 of those participants then paid $1,495 for three-day real estate seminars, and nearly 800 paid up to $35,000 for all-inclusive packages that included one-on-one mentoring.   Trump University changed its name to the Trump Entrepreneur Initiative in May 2010 — the New York State Education Department had deemed the "university" part of the name misleading and, soon after, stopped operating.

The venture is still  caught up in three pending lawsuits, including the $40 million suit brought by New York Attorney General Eric Schneiderman.

Trump's opponents have used the university in recent days to try to put the GOP front-runner on the defensive. Sens. Ted Cruz (R-Tex.) and Marco Rubio (R-Fla.) brought up the controversy in Thursday's debate, and the conservative American Future Fund released three ads on Friday in which Trump University students bashed the program.

On Sunday, Trump defended the school, saying that many of its top instructors were handpicked and that 98 percent of people who took the courses "thought they were terrific."

Sunday wasn't the first time Trump has suggested that a judge related to the Trump University lawsuit had political and/or racial motivations. At a rally Saturday in Betonville, Ark.,  he said of the judge: "I believe he happens to be Spanish, which is fine," Trump said. "He's Hispanic, which is fine."