David M Jackson

USA TODAY

The Republican primaries end Tuesday with an embattled Donald Trump under pressure to tone down his rhetoric, including House Speaker Paul Ryan's statement that the businessman's attacks on a federal judge amount to "textbook" racism.

Trump's claims that a federal judge is biased because of "Mexican heritage" have been likened to Joe McCarthy-like Communist witch hunts, and have prompted pressure on Republican leaders to pull their support of the New York businessman.

"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 Democratic candidate Hillary Clinton, and "I think if we go into the fall as a divided party, we are doomed to lose."

Sen. Bob Corker, R-Tenn., speaking on MSNBC's Morning Joe, said of Trump: "He still has time to pivot — Time is running short, but he has time to do that."

Trump has maintained his attacks on the federal judge hearing a fraud lawsuit against the now-shuttered Trump University, saying his "Mexican heritage" makes him biased against a candidate who has criticized illegal immigration from Mexico.

"It's a civil lawsuit that should have been dismissed a long time ago but the judge is treating me very unfairly," Trump said Monday on Fox News.

U.S. District Judge Gonzalo Curiel is a former federal prosecutor who was born in Indiana. His parents were born in Mexico.

The Manhattan real estate mogul who wrapped up the Republican presidential nomination in early May is scheduled to speak Tuesday night as he claims wins in the final five GOP delegate contests: California, Montana, New Jersey, New Mexico, and South Dakota.

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

Critics, including some Republicans, said Trump's emphasis on the judge's ethnicity amounts to racism.

While many GOP lawmakers have endorsed Trump — if only as the sole alternative to Clinton — they have become increasingly uncomfortable in recent days

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.”

Graham told MSNBC he will not vote for either Trump or Clinton in the general election, and said he is looking for a write-in candidate.

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.

Former U.S. Rep. Joe Scarborough, R-Fla., now the host of MSNBC's Morning Joe, said on the program Tuesday that Republicans need to reconsider their support of Trump, or risk losing control of the House and Senate in the fall elections.

"Republicans, call him out, back away from those endorsements," Scarborough said. "Make him back down on the Muslim ban. Make him back down on this racist comment that he's made about a man born in Indiana saying he's incapable of being a fair judge."

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.

As for Trump, Christie said “it’s refreshing to have somebody who’s willing to speak their mind and is not reading from a script.’’

Trump himself says his campaign will prevail in the long run.

"I want to focus on the economy, I want to focus on the military," Trump said on Fox News. "I want to focus on things that we need to focus on. Not a civil lawsuit that I'm going to end up winning anyway."