Republicans and Democrats alike are slamming Donald Trump for his comments about a federal judge. Here are six times something Trump said made sparked a huge backlash from critics. (Sarah Parnass/The Washington Post)

Donald Trump finds himself increasingly isolated over his persistent attacks on the ethnicity of a Hispanic federal judge, as Republicans moved en masse Monday to disassociate themselves from the remarks while Democrats worked to tie the entire Republican Party to them.

The attacks on U.S. District Judge Gonzalo Curiel — who Trump says is unfit to hear two lawsuits against Trump University because of his “Mexican heritage” — threaten to erode the real estate mogul’s tepid support within the Republican establishment, which has cautiously fallen behind him in recent weeks.

GOP lawmakers and strategists face uncomfortable questions about how they can support Trump without also tacitly endorsing his criticism of Curiel and his remarks that a Muslim judge might also be questionable. Some Republican lawmakers arriving Monday on Capitol Hill scurried from reporters to avoid answering questions about the remarks; others condemned the comments as wrong while saying they would still support Trump as the Republican nominee.

One of the strongest criticisms came from Sen. Susan Collins of Maine, who has said that she plans to support the presumptive GOP nominee. “His statement that Judge Curiel could not rule fairly because of his Mexican heritage does not represent our American values,” Collins said in a statement. “Mr. Trump’s comments demonstrate both a lack of respect for the judicial system and the principle of separation of powers.”

The episode has distracted from the Trump campaign’s efforts to unite the party ahead of a competitive general-election bid against rival Hillary Clinton, who has secured the delegates necessary to win the Democratic nomination. Democrats hope to use his comments — the latest in a series of attacks and proposals that have infuriated Hispanic voters — to paint the entire Republican Party as out of touch with minorities.

Sen. Susan Collins (R-Maine), shown here in a file photo, said Donald Trump’s claim that a Latino judge cannot treat him fairly because of his border proposals “does not represent our American values.” (J. Scott Applewhite/AP)

Clinton said Monday during a campaign appearance in suburban Los Angeles that his remarks are contrary to American values.

“I’m waiting for him to say, because of the bigoted things he has said about women, that a woman judge couldn’t fairly preside over a case,” Clinton said. “By the time he’s finished, nobody is going to be left in this country that he is going to have exempted from insults. We need to stop this divisiveness, this bullying and bigotry.”

Republican sources said there have been multiple efforts in recent days to convey displeasure to Trump and his senior advisers, urging Trump to pull back on his assault. The entreaties have included major GOP donors and Republican National Committee Chairman Reince Priebus.

Trump has resisted those recommendations. Instead, he has responded the way he often does when challenged: by digging in harder than ever. “If somebody else were there, this would have been thrown out on summary judgment,” Trump said about Curiel in a Fox News interview Monday, adding: “All I’m trying to do is figure out why I’m being treated so unfairly by a judge.”

The issue has also caused turmoil and infighting within the Trump campaign. In a conference call Monday, the real estate mogul told surrogates to step up their attacks on Curiel as biased and on reporters as racists, overriding a directive from his own staff distributed over the weekend, according to a report by Bloomberg News.

“Are there any other stupid letters that were sent to you folks?” Trump said, according to the report. “That’s one of the reasons I want to have this call, because you guys are getting sometimes stupid information from people that aren’t so smart.”

Inside the party, there are growing concerns about Trump’s temperament, his willingness to work with other Republicans, and his ability to admit errors. That leaves the party in a precarious and politically risky position as they head to the July convention in Cleveland, and it has emboldened anti-Trump voices who have been criticized for not falling in line. “Public Service Announcement: Saying someone can’t do a specific job because of his or her race is the literal definition of ‘racism,’ ” Sen. Ben Sasse (R-Neb.) wrote Monday on Twitter.

The episode has again highlighted Trump’s resistance to being managed, particularly by party strategists who typify the conventional political establishment. “The more you tell him not to do something, the more he wants to do it,” said a GOP strategist who has been dealing with some of the fallout.

With little other recourse, prominent Republicans hope that eventually this episode will wear itself out and the campaign will move on. “He’s got to get past this,” a senior Republican said. “It’s not going to get fixed in the short run.”

Even some loyal Trump supporters have struggled to rationalize his remarks. Former House speaker Newt Gingrich, a vocal Trump ally and informal adviser, blasted the Republican nominee Sunday, calling his comments about the judge’s ethnicity “inexcusable.” But after Trump called that criticism “inappropriate” on Monday, Gingrich softened his tone.

Gingrich said Monday that “focusing on ethnicity” in his remarks was not legitimate but that “Trump’s complaints about the judge and the law firm in the Trump University case are valid and reflect a growing pattern of politicized ‘justice.’ ” He added, “I am confident the Trump campaign, from the convention on, will be remarkably inclusive and will do much better with minorities than [Mitt] Romney did in 2012.”

Rep. Chris Collins (R-N.Y.), one of Trump’s key liaisons on Capitol Hill, sought to defend Trump against accusations of racism while maintaining distance from his comments.

“I don’t view them in the racist context because I don’t believe Donald Trump is a racist. . . . He has used words I would not have used, but that does not mean his frustration isn’t real, that he does not believe this judge is biased,” Collins said in an interview on CNN.

Many GOP lawmakers had hoped that Trump would begin to show more discipline as he pivoted to the general election, focusing on his populist economic message rather than becoming embroiled in endless controversies as he did in the primary.

Trump has not lived up to those hopes.

Sen. Jeff Flake of Arizona, a Republican who has kept his distance from Trump, said Monday morning on MSNBC that he would continue to withhold his endorsement. Trump’s attacks on Curiel went to “a whole new level,” he said.

“It’s not just ill-informed or ignorant statements, but they suggest that when he’s president after November, that perhaps he ought to go after that judge,” Flake said. “It’s very disturbing.”

Several of Trump’s former primary rivals — including Sen. Ted Cruz (R-Tex.), Sen. Marco Rubio (R-Fla.) and Ohio Gov. John Kasich (R) — also weighed in.

“Of course it is inappropriate to be attacking a federal judge’s race or ethnicity,” Cruz said Monday. He declined comment when asked if the issue weakens his faith in Trump’s ability to select federal judges: “You’re going to have to ask Donald to explain why he says what he says.”

Rubio, who endorsed Trump, said in an interview Monday with WFTV-TV in Orlando that Curiel “is an American, born in the U.S., a judge who has earned that position. I don’t think it reflects well on the Republican Party. I don’t think it reflects well on us as a nation.”

He added, “I ran for president, and I warned this was going to happen.”

Meanwhile, Democrats in competitive races across the country are seeking to use Trump’s comments against their opponents. Katie McGinty, who is challenging Republican Sen. Patrick J. Toomey in Pennsylvania, blasted the senator for not speaking forcefully against Trump. “It is profoundly disappointing that Pat Toomey has chosen to remain silent and on the sidelines instead of stepping forward and condemning Donald Trump,” she wrote Monday in a statement.

In Maryland, GOP Senate candidate Kathy Szeliga distanced herself from Trump’s comment’s Monday, calling his screeds against Curiel “racist” and “insulting to all Americans.”

“My own daughter-in-law is of Mexican descent,” she wrote on her Facebook page. “To say that anyone’s ethnic background should disqualify them from public service of any kind — particularly a judge who has sworn an oath to uphold the Constitution of the United States — is, by definition, a racist statement.”

Dan Balz, Paul Kane and Chris Cillizza contributed to this report.