Senate Foreign Relations Chairman Bob Corker on Thursday lambasted Donald Trump, saying the president is driving the United States toward “great peril” because he lacks the “stability” and “competence” for the country’s highest office.

The Tennessee Republican once appeared on stage at a Trump campaign rally, but it any goodwill he might have built with Trump likely evaporated Thursday. The president, as he did with a Twitter attack earlier in the day on Sen. Lindsey Graham, R-S.C., often attacks any critics — and holds grudges.

“The president has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful,” Corker said during an interview that was posted on Facebook.

“He also, recently, has not demonstrated that he understands the character of this nation,” Corker added, apparently referring to the recent racially tinged violence in Charlottesville, Va. “He has not demonstrated that he understands what has made this nation great and what it is today. … And without the things that I just mentioned happening, our nation is going to go through great peril.”

Corker once was considered a candidate for secretary of state — even vice president — under Trump. But on Thursday, he said Trump must find “way more discipline” and “a lot more inner strength” in order to “be measured and to try to solve problems.”

“Radical changes” must “take place, at the White House itself,” Corker said. “It has to happen. The president needs to take stock of the role he plays in our nation and move beyond himself — move way beyond himself. And move to a place where, daily, he’s thinking about what’s best for our nation.”

Two senior White House spokeswomen had not responded to a request for comment about Corker’s remarks. 

Corker’s comments show just how frustrated many congressional Republicans, especially in the Senate, are growing with Trump.

Trump, just over 200 days into his term, often appears mostly concerned with how he is perceived, his and his family’s brand and the far-right political base he will need to win reelection in 2020. That means he often lashes out at lawmakers he needs to pass legislation to enact his policy agenda — which would go a long way to helping his expected re-election bid.

On Thursday morning, Trump went after Graham and GOP Sen. Jeff Flake, R-S.C., two key votes on issues like health care and taxes. Trump accused Graham or a “disgusting lie” for saying Trump’s controversial Tuesday comments defending some white supremacists amounted to the president drawing a “moral equivalency” between pro-white racists and counter-protesters like Heather Heyer, who was killed in Charlottesville when a Nazi sympathizer rammed his car into a crowd of her ilk.

And he praised Flakes Arizona GOP primary foe while saying the senator is “WEAK on borders, crime and a non-factor in Senate. He’s toxic!”

Corker defended Flake, calling him “one of the finest human beings I’ve ever met” and advising White House officials to “embrace the character, the substance of someone like Sen. Flake.”

“He’s one of the finest people I serve with. He’s got a conscience. He’s a real conservative, he’s a real conservative,” the Corker said in his  signature Tennessee drawl. “I hope for the good of our country he’ll be someone who’ll be serving our country after 2018.”

Corker called the white supremacist events, violence and subsequent fire storm in Charlottesville “repugnant.”

“And anything that’s done to incite or cause a movement — white supremacy group, KKK, neo-Nazi group — anything that’s said to make them feel that their standing in our nation is enhanced is repugnant,” Corker said in a thinly veiled message to Trump.

On Tuesday, Trump repeatedly praised what he contended were “very fine” white protesters.

“But not all of those people were neo-Nazis, believe me. Not all of those people were white supremacists, by any stretch,” the president said, not explaining how he reached that conclusion. “Those people were also there because they wanted to protest the taking down of a statue [of] Robert E. Lee.”

Some of the white nationalist groups were there to “legally” and “innocently” protest, the president said, contended the counter-protesters lacked a permit while the pro-white groups obtained one. Trump also labeled the counter-protestors as “vicious” and “very violent.”

Corker said the president has yet to “appropriately” address the country on the Charlottesville situation.

“I think that sometimes he gets in a situation where he double[s] down to try to prove — to try to make a wrong a right,” Corker said in his typically blunt fashion. “I think he’s done that in this case. I would ask that he take stock of who he is as president of all the people in our nation.”