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WASHINGTON — A prominent Republican senator delivered a stinging rebuke Thursday of Donald Trump's short time in office, declaring he has not shown the stability or competence required for an American president to succeed.

Sen. Bob Corker of Tennessee, chairman of the Foreign Relations Committee, also said Trump "recently has not demonstrated that he understands the character of this nation." During comments to local reporters after a speech to the Chattanooga Rotary Club, Corker called for "radical changes" in how the Trump White House operates.

His remarks, which were posted on Facebook, came two days after Trump declared at a New York press conference that white supremacists don't bear all the blame for the violence last weekend in Charlottesville, Virginia. The president's remarks have triggered a firestorm of protest, with a number of Republicans criticizing Trump for giving weight to the complaints of white nationalists by refusing to definitively condemn them.

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Corker has sought to be a strong supporter of Trump's, particularly on foreign policy matters. But Trump's impulsive and often bombastic style has complicated the relationship for Corker and other congressional Republicans. A few months ago, following reports that Trump had disclosed highly classified information to a pair of Russian diplomats in the Oval Office, Corker said the White House was "in a downward spiral."

Sen. Bob Corker. Michael Reynolds / EPA

But Corker in recent weeks had largely declined to answer questions about Trump's tweets or other political drama, telling reporters covering Congress that he was focused instead on matters of policy.

He elected to weigh in Thursday, however. Noting that the country is polarized, Corker said, "Helping inspire divisions because it generates support from your political base is not a formula for causing our nation to advance, our nation to overcome the many issues that we have to deal with right now."

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Corker said, "The world needs for our president to be successful," and said he's hopeful Trump will do what's necessary to bring out the best in people, regardless of their political affiliations.

Trump, he said, needs "to take stock of the role that he plays in our nation and move beyond himself, move way beyond himself, and move to a place where daily he's waking up thinking about what is best for our nation."

Corker also defended his Republican colleague, Sen. Jeff Flake of Arizona. On Twitter Thursday, Trump called Flake "toxic" while praising his primary election opponent.

Flake is "one of the finest best human beings I've ever met," Corker said. He said the White House would be well served to embrace Flake because of his substance and character.

Flake has a "conscience and is a real conservative," Corker said.