Sen. Bob Corker, R-Tenn., said Thursday that President Trump has yet to show he has the competence needed to be a successful president, and doesn't understand the character of the nation.

"I do think there need to be some radical changes. 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. And we need for him to be successful," Corker told reporters after a Chattanooga Rotary Club meeting Thursday. "Our nation needs for him to be successful. It doesn't matter whether you're a Republican or Democrat. We need for our president — the world needs for our president — to be successful."

Corker condemned Trump for his "hot rhetoric" on North Korea last week, and for attacking fellow Republicans on Twitter, as Trump did Thursday morning when he criticized Republican Sens. Jeff Flake of Arizona and Lindsey Graham of South Carolina.

The Tennessee Republican also criticized the president's comments about the violence in Charlottesville, Va., this week, where white nationalist groups clashed with counter-protesters. In an impromptu press conference Tuesday, Trump blamed the violence on "both sides," and said there were "very fine people" who gathered in Charlottesville to protest.

"He also recently has not demonstrated that he understands the character of this nation," Corker said. "He has not demonstrated that he understands what has made this nation great and what it is today, and he's got to demonstrate the characteristics of a president who understands that. And without the things that I just mentioned happening, our nation is going to go through great peril."

Corker is one of several Republicans who spoke out against Trump's remarks on the violence in Charlottesville this week.

Earlier Thursday, Sen. Dan Sullivan of Alaska urged the president to issue a "complete and unambiguous condemnation" of white nationalist groups.

"Anything less than complete & unambiguous condemnation of white supremacists, neo-Nazis, and the KKK by the @POTUS is unacceptable. Period," Sullivan tweeted.

Though Trump's comments drew the ire of his fellow Republicans, Corker is the first to offer such a blunt assessment of the president. The Tennessee Republican urged Trump to unite the country, rather than speak only to his base.

"We should hope that he aspires, that he does some self-reflection, and that he understands what is necessary to demonstrate stability, to demonstrate competence, to demonstrate he understands the character of our nation and works daily to bring out the best from the people of our nation," Corker said. "Helping to inspire divisions because it generates support from your 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."