Republican Illinois Sen. Mark Kirk announced he is not supporting Trump for president based on his comments about U.S. District Court Judge Gonzalo Curiel.

This is a reversal for Kirk, who said in March he would support Trump.

“While I oppose the Democratic nominee, Donald Trump’s latest statements, in context with past attacks on Hispanics, women and the disabled like me, make it certain that I cannot and will not support my party’s nominee for president regardless of the political impact on my candidacy or the Republican Party,” Kirk said in a statement. “I have concluded that Donald Trump has not demonstrated the temperament necessary to assume the greatest office in the world.”

Kirk is locked in a tough reelection battle against US Democratic Representative Tammy Duckworth, whose campaign has repeatedly tried to link Kirk with Trump.

On Tuesday, Trump asserted that his comments were being “misconstrued” but did not back down or apologize for saying repeatedly that Curiel could not preside fairly over a case involving Trump University because of his Mexican heritage.

Trump provided a written statement on the matter late Tuesday.

“It is unfortunate that my comments have been misconstrued as a categorical attack against people of Mexican heritage. I am friends with and employ thousands of people of Mexican and Hispanic descent. The American justice system relies on fair and impartial judges. All judges should be held to that standard,” Trump stated. “I do not feel that one’s heritage makes them incapable of being impartial, but, based on the rulings that I have received in the Trump University civil case, I feel justified in questioning whether I am receiving a fair trial.”

Curiel was appointed a U.S. District Court Judge in San Diego in November 2011 by President Barack Obama.

It’s in that role that Curiel is handling the class-action lawsuit involving Trump University.

Greg Vega is a longtime attorney in San Diego who grew up with Curiel in East Chicago, Indiana. Both served as federal prosecutors in California. Vega says he is best friends with Curiel and speaks to him daily.

“I am confident that he [Curiel] is not reading, listening or watching anything on this matter. I am confident that both Mr. Trump and the plaintiffs in the Trump University case will get a fair trial,” Vega told KPBS Public Radio in San Diego.

Dr. Jorge Benavente, an optometrist in Munster, Indiana, and a longtime friend of the judge, agrees.

“You know Trump is ignorant and doesn’t know what he’s talking about. Gonzalo has dedicated his life to the law,” Benavente said. “I don’t think Donald Trump is going to bother him.”

Kirk is the first leading Republican to publicly disavow earlier support for Trump, but others, like House Speaker Paul Ryan, have joined in denouncing Trump’s attack on the judge.

“I regret those comments he made. Claiming a person can’t do their job because of their race is sort of like the textbook definition of a racist comment,” Ryan said at a news conference where his attempts to focus on a new House GOP poverty-fighting agenda were overwhelmed by questions about Trump. “I think that should be absolutely disavowed. It’s absolutely unacceptable.”

“But do I believe Hillary Clinton is the answer? No, I do not,” Ryan said.

Pat Brady, former head of the Illinois Republican Party, said Kirk is “100 percent spot on” with his decision.

“Mark [Kirk] is a military man and he’s a country-first guy so you’d expect that Senator Kirk at some point would come to this conclusion, and I think the tipping point was just the last week or 10 days” Brady said. “I don’t think Senator Kirk’s support of Donald Trump has ever been strong. When you’re in a political party, you gotta support your nominee until it’s apparent that a guy like Donald Trump being president is just bad for the country and he shouldn’t be supported.”  

The Associated Press contributed to this report.