Former Speaker of the House Newt Gingrich is a noted fan of presumptive Republican presidential nominee Donald Trump, but Gingrich said Sunday the businessman’s comments about a federal judge’s Mexican heritage crossed the line.

“This is one of the worst mistakes Trump has made,” Gingrich said on Fox News Sunday.”I think it’s inexcusable.” Trump has said he thinks Judge Gonzalo Curiel is biased against him because of Curiel’s ethnicity.

Curiel, who is the presiding judge in a lawsuit against Trump University, was born in Indiana but his parents are from Mexico. Trump has long proposed that he would build a border wall along the U.S.’s southern border with Mexico and he seems to think that proposal would make Curiel an unfit match for the case.

Gingrich did not call the Republican candidate’s comments racist, saying that he has every right to criticize a judge, but he told Fox News Sunday the statements were sloppy and said that Trump should know better.

“He is an American. Period. When you come to America, you get to become an American, and Trump, who has grandparents who came to the U.S., should understand this as much as anybody,” Gingrich said.

On Monday, Trump responded to Gingrich’s comments, calling them “inappropriate” in an interview. The businessman said he has to defend himself against attacks on Trump University.

“You have to respond,” Trump said Monday. “All I’m trying to do is figure out why I’m being treated so unfairly by a judge.”

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