Presumptive GOP nominee Donald Trump doubled down Friday on attacking a federal judge for his ethnicity and argued that U.S. District Judge Gonzalo Curiel should recuse himself from cases involving scandal-plagued Trump University.

In an interview with CNN’s Jake Tapper, Trump insisted Curiel’s ethnicity means he can’t be an impartial judge in matters involving him because of his immigration policy.

“I’ve had terrible rulings, I’ve been treated very unfairly. Now, this judge is of Mexican heritage,” Trump began. “I’m building a wall. I’m building a wall.”

“So no Mexican judge could ever be involved in a case that involves you?” Tapper asked.

Trump replied that Curiel is a member of a very “pro-Mexico” group, saying “that’s all fine” but he should recuse himself from the cases.

Tapper again pressed Trump on his personal attacks. “You’re invoking his race talking about whether or not he can do his job,” he said.

“Jake, I’m building a wall. OK? I’m building a wall. I’m trying to keep business out of Mexico. Mexico’s fine!” he said.

Tapper reminded Trump that Curiel, who was born in Indiana, is American.

“He’s of Mexican heritage and he’s very proud of it, as I am,” Trump replied.

Later on, Tapper again asked Trump if invoking Curiel’s heritage is necessary in criticizing the judge’s handling of the case, to which the real estate mogul said, “I think that’s why he’s doing it.”

He tried to spell it out again for Tapper, saying, “We are building a wall. He’s a Mexican. We’re building a wall between here and Mexico.”