Donald Trump is again causing major alarm for Republicans - and they're calling him out

John Kasich has remained mostly quiet since dropping out of the presidential race in May.

But he apparently couldn't sit on the sidelines any longer.

"Attacking judges based on their race &/or religion is another tactic that divides our country," the Ohio governor tweeted Monday morning. "More importantly, it is flat out wrong."

Donald Trump, the now-presumptive GOP nominee, has spent the last few days lambasting a federal judge for being unfair in presiding over a Trump University case because of his Mexican heritage.

US District Judge Gonzalo Curiel, was born and raised in Indiana. But that has mattered little to Trump.

"Now, this judge is of Mexican heritage," Trump said during a recent interview with CNN's Jake Tapper. "I'm building a wall, OK? I'm building a wall. I am going to do very well with the Hispanics, the Mexicans."

Kasich, for his part, called on Trump to apologize.

"@realDonaldTrump should apologize to Judge Curiel & try to unite this country," he subsequently posted.

Kasich joined what's becoming a long line of Republicans who've condemned the Manhattan businessman for his latest inflammatory remarks. So many that the campaign for Democratic frontrunner Hillary Clinton, who's repeatedly chastised Trump for the continued comments, cut a video of Republicans calling out Trump.

".@realDonaldTrump's bigoted comments about a Latino judge are so disgusting, even other Republicans are offended," Clinton's campaign tweeted.

'Couldn't disagree more'

Mitch McConnell and Paul Ryan, the highest-ranking GOP leaders in the Senate and House, respectively, both condemned Trump's attacks. So did former House Speaker Newt Gingrich and Tennessee Sen. Bob Corker, who have both been floated as potential Trump running mates, and Jeff Flake, an Arizona senator who, like Kasich, has yet to endorse his party's presumptive presidential nominee.

In a Sunday interview on NBC's "Meet the Press," McConnell said he "couldn't disagree more" with what Trump has said.

"This is a man who was born in Indiana," McConnell said. "All of us came here from somewhere else."

And just one day after ending his month-long endorsement standoff with Trump, Ryan distanced himself from the racially charged remarks in a Friday interview with WISN radio host Vicki McKenna.

"Look, the comment about the judge the other day just was out of left field for my mind," Ryan told McKenna. "It's reasoning I don't relate to, I completely disagree with the thinking behind that."

"He clearly says things I do not agree with, and I've had to speak up from time to time when that happens," Ryan said, adding that he will continue to do so if necessary.

Corker, who recently visited Trump at Trump Tower and has received increased attention as a potential running mate, told George Stephanopoulos on ABC's "This Week" that he did not "condone" Trump's attacks, but insisted on moving on to another subject.

Even Trump's own campaign reportedly wants the attacks to stop. In an eyebrow-raising MSNBC report Monday morning - one that caused Trump to go on an extended Twitter rant - the outlet reported that Trump "rebuffed efforts" from his campaign, donors, and party officials to back away from the attack because he "was unwilling to look like he had caved to pressure."

"These are things that will defeat [us]," a source within the campaign told MSNBC.

Trump did manage to receive some backup from the former US attorney general under President George W. Bush, Alberto Gonzales. But it was nowhere near enough to counterbalance the roaring pushback from the GOP.

The loudest roars arguably came from Gingrich and Flake.

'One of the worst mistakes'

Gingrich, who has served as something of a Trump surrogate in recent months, called it "one of the worst mistakes" the real-estate magnate has made and added that it's "inexcusable."

"First of all, this judge was born in Indiana," Gingrich told "Fox News Sunday" host Chris Wallace. "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 US, should understand this as much as anybody."

He continued:

Second, to characterize, you know - if a liberal were to attack Justice Clarence Thomas on the grounds that he's black, we would all go crazy. Every conservative would say it was wrong and it was racism. And Trump has got to, I think, move to a new level. This is no longer the primaries. He's no longer an interesting contender. He is now the potential leader of the United States and he's got to move his game up to the level of being a potential leader.

Although he did not answer whether he believed the attack to be racially motivated, Gingrich said he hoped "it was sloppiness" and said Trump's assertion of having "many Mexican friends" is "irrelevant."

"This judge is not Mexican," he continued.

Trump on Monday called Gingrich's comments "inappropriate."

'Very disturbing'

Meanwhile, during a Monday-morning appearance on MSNBC's "Morning Joe," Flake, a vehement critic of Trump, called this latest firestorm "a whole new level" and "very disturbing."

"If this doesn't change, we're in for big trouble," Flake said.

"Because it's not just ill-informed or ignorant statements, but they suggest that once he's president after November, that he should go after that judge," he continued.

Saying Trump is "not his first choice or his 17th choice" for the presidency, he said Trump's pitting of races, genders, and cultures against each other is everything the GOP stands against.

"The whole thing that we Republicans say we're against are identity politics," he said. "That if you're a certain gender or you're a certain race, then you have to vote that way. He's just trying to confirm that stereotype that's completely wrong and it's offensive and this week it was a whole new level."

During his interview with Tapper, Trump repeatedly denied his rationale was "racist." But he hammered home several times the argument that Curiel's heritage causes him to view the Trump University cases unfairly because he is planning on "building a wall" along the US-Mexico border.

"Jake, I'm building a wall," Trump said. "I'm building a wall. I'm trying to keep business out of Mexico. Mexico's fine. ... He's of Mexican heritage, and he's very proud of it, as I am of where I come from."

Trump took his argument a step further Sunday. Asked by John Dickerson on CBS' "Face the Nation" whether he believes a Muslim judge would also treat him unfairly, because of his proposal to bar Muslim immigrants and tourists from entering the country, Trump said "it's possible."