Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE read from a teleprompter, dialed back the schoolyard insults and tried to sound more measured and presidential during his speech Tuesday night.

GOP lawmakers applauded the effort, but they aren’t sure it will last.

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“If past history is an indicator of what will happen in the future, [Trump] will restrain himself for a day because he feels he overstepped the line,” said Rep. Reid Ribble Reid James RibbleFormer Sen. Tom Coburn dies at 72 Ex-GOP lawmakers side with NY in Supreme Court case over Trump tax returns Former GOP lawmakers, officials ask court to enforce House subpoena on McGahn MORE (R-Wis.), “and then he’ll go back and he’ll say something outlandish.”

A day after Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) rebuked Trump’s attack on a federal judge as “racist,” Republicans on Capitol Hill openly fretted about what the brash New York billionaire might say — or which group he might offend — next.

Trump’s remark that U.S. District Court Judge Gonzalo Curiel cannot be impartial in a Trump University case because “he’s a Mexican” has roiled the 2016 race, dominating the news cycle for the past week.

“When he acts out in this outlandish way, it gives Republican voters a great deal of pause on the legitimacy of his candidacy,” said Ribble, who is close to Ryan and has refused to endorse Trump.

An anti-immigration hardliner, Trump’s race-based attacks on the judge continued to reverberate on Capitol Hill on Wednesday, a week after they were first uttered by the real estate mogul turned presumptive GOP presidential nominee.

Republicans in tough reelection races, including Sen. Rob Portman Robert (Rob) Jones PortmanRomney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery House passes B bill to boost Postal Service MORE (R-Ohio), are pushing Trump to apologize and retract his racially charged comments about the Indiana-born judge. “I’ve said he ought to retract,” Portman told The Hill.

Rep. Bill Flores William (Bill) Hose FloresPatient Protection Pledge offers price transparency Texas GOP lawmaker calls for 'carbon neutral' but 'energy dominant' future OVERNIGHT ENERGY: Biden calls climate change one of America's four major crises | National parks chief says coronavirus staff shortages shouldn't prevent access | Trump hits California officials over wildfires MORE (R-Texas), head of the 170-member conservative Republican Study Committee, said Wednesday he wasn’t ready to back Trump, saying he was “incredibly angry” to see Trump raise questions about the judge’s impartiality “because of his ethnicity.”

“Americans need to see more vision and less trash talk,” Flores said in a statement.

House GOP Policy Committee Chairman Luke Messer (R-Ind.), who is backing Trump, said the candidate’s attack on Curiel was particularly offensive to him given that “the judge in question is a Hoosier.”

Trump’s “acceptance speech was encouraging but his comments on the judge were terrible, they are inappropriate, and they undercut his ability to get elected,” Messer told The Hill. “If he doesn’t stop this stuff, he’s not going to have a shot at being elected president.

“And I, for one, don’t want to see a President Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE.”

The topic of Trump also briefly came up at the top of a closed-door meeting of House Republicans in the basement of the Capitol.

Ryan, during his leadership update, said he endorsed Trump last week — after a lengthy holdout — because Trump, not Clinton, would give congressional Republicans the best opportunity to turn their policies and ideas into law, according to sources in the room.

But Ryan also said he wouldn’t hesitate to speak out when he feels Trump has crossed the line and violated core conservative principles. During a news conference on poverty Tuesday in an African-American neighborhood in D.C., the Speaker lashed out at Trump’s attacks on the judge as “indefensible” and the “textbook definition” of racism — a rebuke Ryan later told his GOP colleagues he hoped would put the controversy to rest and allow Republicans to pivot back to their election-year agenda project.

Ryan’s full-throated rebuke “needed to be done. It was professionally handled. It was respectful of everyone,” said Rep. Joe Wilson Addison (Joe) Graves WilsonDemocrats raise alarm about new US human rights priorities Democrat Teresa Leger Fernandez defeats Valerie Plame in New Mexico primary Trump campaign launches new fundraising program with House Republicans MORE (R-S.C.), who found himself in the center of his own race controversy after shouting “You lie!” at President Obama during a healthcare speech in 2009.

Trump has offended and outraged Hispanic groups since he kicked off his presidential campaign last summer at a Trump Tower event by calling Mexican immigrants “rapists” and criminals while vowing to build a wall on the southern border.

Later, he mocked Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.), who was tortured for years in a Viet Cong prison, as no war hero; proposed banning Muslims from entering the U.S.; mocked a reporter with a disability; and disparaged the physical appearance of numerous women.

“That’s been a problem with the presumptive nominee for some time. He makes all these incendiary comments and lacks policy specifics,” said Rep. Charlie Dent (R-Pa.), a backer of John Kasich’s failed bid who still has not endorsed Trump. “We’ve heard this before on Mexicans, Muslims women, POWs, the disabled.

“His comments [on Curiel] will make it more likely that members who were disinclined to endorse him will be even more disinclined to endorse him,” Dent added.

For vulnerable GOP Sen. Mark Kirk Mark Steven KirkLiberal veterans group urges Biden to name Duckworth VP On the Trail: Senate GOP hopefuls tie themselves to Trump Biden campaign releases video to explain 'what really happened in Ukraine' MORE, the racial attacks against Curiel were the final straw. The vulnerable senator from deep-blue Illinois rescinded his endorsement on Tuesday.

Others say they hope Trump changes his tone and rhetoric, but they’re not holding their breath.

“I hope he changes but it’s tough to change,” said Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.), who represents a border state with a large Hispanic population and who also has not endorsed Trump.

“There’s no evidence from his record as a businessman that he’s been discriminatory — that’s what makes me hope he’ll change. But if he’s doing it just for effect, to drive a wedge, then it’s almost worse, so I don’t know.”

Flake said he still doesn’t understand why Trump has not dialed back some of that rhetoric as he heads into the general election.

“He felt the Muslim ban played to his political benefit in the primary,” Flake said, “but you’ve got to pivot pretty hard and he hasn’t yet.”

Ribble agreed that Trump hasn’t proven he can be a viable general election candidate.

“He’s engaged the activists, but what’s going to happen when the normal American, the regular American sits and watches what’s on TV? How are they going to respond?” Ribble said. “And I think that is the real test about whether he can change.

“Who is the real Trump? Is he the racist xenophobic guy, or is he now this new pretend guy? Where is the genuineness?”