David Jackson

USA TODAY

Presumptive Republican presidential nominee Donald Trump defended his comments about a federal judge Tuesday while facing the prospect of a revolt by GOP lawmakers who say his racially charged rhetoric will cost them elections up and down the ballot.

"We're only getting started, and it's going to be beautiful," Trump told supporters gathered at his golf club in Briarcliff Manor, N.Y., to celebrate victory in the last five Republican primaries of the year, wrapping up his remarkable run to the GOP nomination.

Trump spoke amid rising criticism from fellow Republicans; one GOP senator, Mark Kirk of Illinois, became the first prominent lawmaker to rescind his endorsement of Trump on Tuesday, citing his attacks on the ethnicity of Gonzalo Curiel, a federal judge who is presiding over a fraud case against the New York businessman.

Illinois Sen. Mark Kirk says he won't support Trump

The GOP nominee "has not demonstrated the temperament necessary to assume the greatest office in the world," said Kirk, who faces a tough re-election race back in Illinois.

As Kirk and other Republicans criticized him, Trump issued a statement earlier in the day saying his comments about the judge have been "misconstrued."

"I do not feel that one’s heritage makes them incapable of being impartial," Trump said, "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."

The businessman did not apologize, and he used a nearly 700-word statement to argue his side of the lawsuit. He ended by noting that a trial is scheduled for November, and "I do not intend to comment on this matter any further."

House Speaker Paul Ryan, R-Wis., said Trump's comments about Curiel's heritage amount to "textbook" racism, though he said he would continue to support the businessman over Democratic candidate Hillary Clinton. Other Republicans said they cannot back Trump and even suggested the possibility of a challenge at next month's convention.

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“As of now, unless he changes significantly, I can’t see myself voting for Donald Trump,” said Sen. Jeff Flake, R-Ariz., a longtime opponent of Trump. Flake told the Associated Press that while there's no talk of a convention challenge at this point, Trump's comments about the judge presiding over a lawsuit against him "might spur it."

Seeking to turn the page from the flap over the judge, Trump used his prepared speech on Tuesday night to launch a political assault on presumptive Democratic nominee Hillary Clinton, saying that the former secretary of State and former President Bill Clinton have "turned the politics of personal enrichment into an art form." He accused them of "selling access, selling favors."

Trump also made a direct appeal to supporters of Clinton's primary rival, Vermont Sen. Bernie Sanders, telling them that "we welcome you with open arms."

Using a teleprompter to help him deliver his speech, instead of his usual ad lib remarks, Trump said some believe he fights too much, but "my preference is always peace." When a fight is necessary, Trump said, "I will never, ever back down," and he pledged to be a "champion" for middle-class Americans who have seen their jobs move overseas.

In claiming the party nomination, Trump said: "I understand the responsibility of carrying the mantle, and I will never, ever let you down."

Trump struck a more combative note in an interview Tuesday on Fox News, saying "it's okay" if some critical Republicans do not endorse him, and they should "get over it."

Trump has maintained his attacks on Curiel, saying his "Mexican heritage" may influence rulings in a fraud lawsuit against the now-shuttered Trump University, because Trump has criticized illegal immigration from Mexico and wants to build a wall along the U.S. southern border.

In his statement Tuesday, Trump said Curiel has made bad rulings in the case and belongs to legal organizations that are hostile to his candidacy. "Questions were raised regarding the Obama-appointed judge’s impartiality," Trump said. "It is a fair question. I hope it is not the case."

Curiel is a former federal prosecutor who was born in Indiana. His parents were born in Mexico.

"Claiming a person can't do their job because of their race is sort of like the textbook definition of a racist comment," Ryan told reporters Tuesday. "If you say something that's wrong, I think the mature and responsible thing is to acknowledge it."

Still, the Wisconsin Republican said Trump is a better bet than Clinton, and "I think if we go into the fall as a divided party, we are doomed to lose."

Senate Majority Leader Mitch McConnell, R-Ky., said it's time for Trump to stop attacking political rivals and members of minority groups, adding that "we're all anxious to hear what he may say next."

Republicans who have been involved in various anti-Trump efforts said the presumptive nominee's problems have been all too predictable. GOP consultant Liz Mair said a string of Trump comments have alienated Hispanic, African-American and female voters and could win up costing the party control of the House and Senate, this year and in the future.

"He is so repellent to so many demographics," Mair said. "There is a real risk of lasting damage."

Republican strategist Rich Galen said many Republicans will rally around Trump because he is the only alternative to Clinton. The businessman "has sales skills, not political skills," Galen said. "So far his sales skills have carried him. Whether they work in the general election, we'll see."

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Trump, who also called for a temporary ban on Muslims entering the United States, has also questioned whether Muslim judges could be fair.

Sen. Lindsey Graham, R-S.C., calling Trump's judicial attacks "the most un-American thing from a politician since Joe McCarthy," told The New York Times: “If anybody was looking for an off-ramp, this is probably it ... There’ll come a time when the love of country will trump hatred of Hillary.”

McCarthy, a U.S. senator from Wisconsin from 1947 to 1957, led a series of congressional hearings investigating suspected Communists in the federal government. He was censured by the Senate in 1954 and died of hepatitis exacerbated by alcoholism in 1957.

Trump does have defenders among Republicans.

New Jersey Gov. Chris Christie, a potential running mate for Trump, told reporters that the businessman is not a racist. Christie said that Ryan is entitled to his opinion, but criticized Graham as a sore loser to Trump in the GOP presidential race.

Christie, who met with the candidate Tuesday at Trump Tower, told reporters that “it’s refreshing to have somebody who’s willing to speak their mind and is not reading from a script.’’

Chris Christie says Donald Trump is not a racist