Plenty of Republican lawmakers have condemned the violence and bigotry of the Charlottesville rally, without directly naming Trump or his both siderism.  A few, like Lindsey Graham and John McCain have. But no one has yet IMO come out so strongly critical of Trump ‘s capacity for the office and ability to lead the country, so this feels like a major turning point.

Corker has been critical of the White House shit show carnival and led the push for the Russian sanctions Legislation so this is not entirely out of left field, but his criticism is getting sharper and more pointed. 

"The President has not yet been able to demonstrate the stability nor some of the competence that he needs to be successful," Corker said, according to a video posted by local news website Nooga.com
"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," Corker added.
"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 we have to deal with right now," Corker said.